Fenrir.Nightfyre said:
10 PDT on the sword is an assload of haste elsewhere. Trading out Darksteel Cap +1, Melaco Mittens, and Darksteel Leggings +1 for Zelus Tiara, Dusk Gloves +1, and Dusk Ledelsens +1 is 15% haste for 8% PDT. You should at minimum have Goading Belt and Haste spell, so you're looking at a 23% minimum increase in damage plus the gains in attack vs CDC, ODD (exact rate will vary depending on DWing or no and WS frequency), slightly higher base damage, and some DEX. I'm not going to say that one is better than the other, but RDM's CDC damage isn't that great so I could see alternatives at least being competitive, especially if the mob doesn't take reduced damage from Sanguine Blade.
RDM doesn't get native Sanguine Blade, and wouldn't full time PDT unless they were /BLU riding Cocoon. While that's fine for weaker NMs, on anything with the ability to cause some pain you'd be /NIN to conserve MP and lessen the time lost to recasting mitigation spells and cures. The other alternatives are going /Drk or /War, but it would be foolish to give up your defensive abilities on anything beyond fodder mobs.
With uncapped fast cast, easy 50% recasts, Para and Saboteur Slow, it's fairly easy to ride shadows in full haste, and on the whole you spend less time casting than /BLU. In this situation, you wouldn't equip PDT gear unless you were going to take a hit, much like you wouldn't full time MDT against a mob unless you were going to get hit by a spell.
Save the PDT gear for when it's necessary, and gear for haste/atk/acc to make your melee phases more effective. It's also worth noting that beyond the less functional sub job, Sanguine Blade is somewhat annoying to gear for on NMs outside of Abyssea. It's a Str/Mnd WSC but requires a fairly decent fInt in order to be a high dmg option, even on IT's you'll see a visible reduction in dmg when going from a neutral mob to a spell caster. I wouldn't count on it to match the utility of CDC's ws dmg+aftermath on any consistent basis.