Warning: Kinda long grip/StoreTP guide for Scythes and Greatswords. Read it if you're interested etc.
First of all, Sword strap is -3% delay reduction but it also reduces your TP gain per hit, unlike haste..which reduces your delay but does not reduce your original TP per hit.
To put it simply: Sword strap is better if it does not break your X-hit build. If using sword strap breaks your X-hit build, then use pole grip; however, if the StoreTP from Rose strap allows you to/or you need it to reach a lower X-hit build, then Rose strap would be better.
I agree with what Raenryong said in general, but I'm just going to expand a little on that:
(I'll just cover Scythe and GS, since this is a DRK thread)
(possible new relevant StoreTP gear from future updates not taken into account here since we don't know what new gear we'll have available for lv80-99 yet)
Also, when we say...for example: "6hit/5hit rebuild" it basically means that, in this case, going from 0% TP it takes you 6hits to get to 100% TP, but after a Weaponskill (provided that you do not miss the WS)it will take you only 5hits to get back to 100% TP. (The "rebuild portion" is due to the TP returns on WS.)
For those where I listed more than one grip, the one listed first (from left to right) will be the one that may be most beneficial under most or certain conditions. Then the reasons why or when you could use each one etc.
Also, the information below is mostly intended for /sam.(samurai as support job)
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Scythe:
528 delay = Sword strap or Rose strap.
Reason:
You only need at least +16 StoreTP for TP and for WS, for a "true 6hit build/5hit rebuild." Using
Sword strap would put you at a 512 delay and you would need at least +21 StoreTP for TP and WS, for a true 6hit/5hit rebuild, which is just the standard /sam,rajas,and brutal.
The use of Rose strap with a 528 delay scythe will come in play if you're going for a 5hit build (5hit/4hit rebuild).
You need +39 StoreTP for TP and for WS, for a true 5hit build. ("5hit/4hit rebuild")
Or you could do a "pseudo 5hit build."
36StoreTP for a "6hit/4hit rebuild" (not a true 5hit build), as long as you land at least 3hits on Guillotine WS. (The first hit, and 2 extra hits)
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513 delay = Pole grip.
Reason:
You need at least +21 StoreTP for TP and for WS, for a true 6hit/5hit rebuild. If you were to use sword strap here, it would put you at 497 delay...which requires you to have +24 StoreTP for TP and WS, but you cannot use rose strap if you're already using sword strap;however, you could use a StoreTP body or eat storeTP food...but I do not recommend those options in general because STP bodies usually have little to no accuracy compared to other standard bodies, and there's usually better food. Therefore I would stick to Pole grip for 513 delay.
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501 delay = Pole grip, or Rose strap.
Reason:
You need at least +23 storeTP for TP and +22 StoreTP for WS, for a true 6hit/5hit rebuild. Sword strap would put you down to 485 delay and break your X-hit build. Pole grip can be used because with the Standard /sam, brutal, and rajas...you will have +21STP, then as long as you land at least 3hits with Guillotine, you will have a 7hit/5hit rebuild. Alternatively, you can equip the Rose strap if you want the "true 6hit/5hit rebuild."
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Greatsword:
501 delay = Rose strap, or Pole grip.
Reason:
You need at least +23STP for TP and +22STP for WS, for a true 6hit/5hit rebuild. Rose strap would be better in my opinion, since that way you don't sacrifice anything in other slots; however, you can use Pole grip IF you don't have rose strap, and then you can use /sam, rajas, brutal, and then you need 2 more STP for TP (Options could be: either white tathlum, or Chivalrous chain + ecphoria ring, or attila's earring + ecphoria ring), and then you needed +22 STP for WS, so the standard /sam, rajas, brutal, and then use attila's earring for WS too.
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494 delay = Rose strap.
Reason:
You need at least +25STP for TP and for WS, for a true 6hit/5hit rebuild. The way to do this one would just be: /sam, rajas, brutal, and rose strap.. which = exactly +25STP. Rose strap is the clear winner for a 494 delay GS.
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489 delay = Rose strap, or Sword strap.
Reason:
You need at least +27STP for TP and +25STP for WS, for a true 6hit/5hit rebuild. You can do it with: /sam, rajas, brutal, rose strap, and need 2 more StoreTP for TP (Options could be: either white tathlum, or Chivalrous chain + ecphoria ring, or attila's earring + ecphoria ring), and then you needed +25 STP for WS... which would just be /sam, rajas, brutal, and rose strap. Furthermore, another new possible way would be with the new Goading belt.(has StoreTP+5, and haste+5%) You could do: /sam, rajas, brutal, rose strap, and Goading belt which = +30STP, and for WS still just do /sam, rajas, brutal, rose strap. If you do not have the gear necessary to 6hit this weapon, or sacrifice would be too much in accuracy/haste etc with the gear that you do have to make it... then you could use Sword strap and have a 7hit build with 474 delay. (would need +13STP to have a 7hit with 474 delay)
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480 delay = Rose strap, or Sword strap.
Reason:
You Need +30 StoreTP for TP and +20 StoreTP for WS, for a true 6hit/5hit rebuild. The way to to this one would be: /sam, rajas, brutal, rose strap, and the new Goading belt(has StoreTP+5, and haste+5%)for +30STP for TP, and then WS you would have: /sam, rajas, brutal, and rose strap (needed only +20STP for WS, but have to WS in rose strap because you lose TP if you change grips). If you can't get the StoreTP necessary to 6hit a weapon with 480 delay, with little to no sacrifice (namely with the gear mentioned above which included the new Goading belt), then you could wear sword strap for a 7hit build with 465 delay. (would need +18STP to keep a 7hit with 465 delay)
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466 delay = Pole grip, or Sword Strap
Reason:
You need at least +17 StoreTP for TP and for WS, for a true 7hit/6hit rebuild. If you use Sword strap... it would put you at a 452 delay, but then you would need +24StoreTP to have a 7hit build, otherwise, you would be stuck at an 8hit build. Nevertheless, You could possibly do: Sword strap, /sam, rajas, brutal, and the new Goading belt (has storeTP+5, and haste+5%)... for +26StoreTP with a 452 delay while using sword Strap; however, the comparison here would be that if you have velocious/speed belt...it is basically 2% double attack and 1% haste Vs. -3% delay reduction.(2% double attack from Pole grip, and Velocious/speed belt has haste+6% which is one more haste than Goading Belt; the other setup was sword strap's delay reduction -3% and Goading Belt's StoreTP+5, and Haste+5%).
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444 delay = Rose strap, or Sword strap.
Reason:
You need at least +27STP for TP and +26STP for WS, for a true 7hit/6hit rebuild. You can do it with: /sam, rajas, brutal, rose strap, and need 2 more StoreTP for TP (Options could be: either white tathlum, or Chivalrous chain + ecphoria ring, or attila's earring + ecphoria ring),
and then you needed +26 STP for WS, so you would do: /sam, rajas, brutal, rose strap, and then use attila's earring for WS too. Furthermore, another new possible way would be with the new Goading belt.(has StoreTP+5, and haste+5%) You could do: /sam, rajas, brutal, rose strap, and Goading belt which = +30STP, and for WS just do /sam, rajas, brutal, and rose strap. If you do not have the gear necessary to 7hit this weapon, or sacrifice would be too much in accuracy/haste etc with the gear that you do have to make it... then you could use Sword strap and have an 8hit build with 430 delay. (would need +14STP to keep an 8hit with 430 delay)
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(I'm putting these next two together because they both give the same base TP per hit)
430 delay and 431 Delay = Rose Strap, or Sword strap.
Reason:
You need at least 31 STP for TP and 25 STP for WS, for a true 7hit build/6hit rebuild. You could do it with: /sam, rajas, brutal, rose strap, the new Goading Belt(StoreTP+5, and haste+5%), and then one more StoreTP from somewhere (Attila's earring, ecphoria ring, chivalrous chain, or white tathlum), and then you needed +25 storeTP for WS...which would just be: /sam, rajas, brutal, and rose strap. In the case of Ragnarok, the relic GS, which is the 431 delay...you could probably get away with using Aurum cuirass on some mobs(since relic GS has accuracy+20, and now with Magian Trials it actually can have accuracy+25) if you do not have the new Goading Belt. Finally, If you do not have the gear necessary to 7hit this weapon, or sacrifice would be too much in accuracy/haste etc with the gear that you do have to make it... then you could use Sword strap and have an 8hit build with 417 delay if using the weapon with a base delay of 430, or use sword strap and have an 8hit build with 418 delay if using the weapon with 431 delay. (would need +17STP to keep a 8hit with 417 delay or with 418 delay)
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This turned out longer than I expected... but there was no way for me to make this shorter while still giving an explanation or reason to "why" you would use each grip, and "how" you can get the StoreTP needed for certain X-hit builds etc.
A lot of people probably already know this stuff, but hopefully this will help those who didn't know or maybe were just too lazy to calculate it themselves.