I'm a tall fellow (6'6" with a 36" inseam) riding a rather tall bike (65cm). I'm currently running 175mm cranks; I ruined my left crank, so they're different makes with approximately the same profile. According to some calculator that someone linked to a while ago, with my inseam my "optimal" crank length is slightly over 180mm. I'm not expecting additional power out of it or anything, but I figure that I can lower my seat a touch with the longer cranks and that might be nice. (To get correct leg extension at the bottom of the pedal cycle, my seat is pretty high. I'm often waiting at lights and would prefer to keep my butt on the seat without feeling like I'm going to fall over in front of a car or something...)
Anyway, I'm content with mismatched cranks for the moment but have been keeping my eyes open for 180mm cranks at LBS... or should I just replace the 175's?