I happened to be in town so I just tested it instead of looking for it on line:
drk/war:280 attack base
berserk:350
berserk+LR(5/5 merits):418
lr:348
280*1.25*1.25=437
(280*1.25)+(280*.25)=420
tested both ways. lr does not appear to calculate att based on berserk and vice versa.
drk/war:359 attack gear
berserk:448
ber+lr:537
lr:447
both calculate based on attack with gear.
I can't speak for if they calculate based on chaos.
Edit: please let me know if that isn't what you were asking. I've been cleaving in tahrongi for like 11 hours and my brain is almost entirely shut down.