Yeah, the commonly available sizes (170-175) really don't give any proportionality to actual leg length. I'm 6', ride 175's, and haven't gone with anything longer mostly because it means getting four new sets of cranks. It does seem ridiculous that we spend so much time getting other aspects of bike fit right, but all ride pretty much the same cranks. 2.5mm difference is not a real adjustment. I think the french company TA make a selection of decent lengths.
One issue to consider is that frame manufacturers don't really allow for the use of cranks beyond the standard range, so pedal clearance in corners may be reduced. Unless of course you get a lovely frame made for you with plenty of BB clearance. Also if you ride track, I think many indoor velodromes require 170mm cranks, so you'll have to get used to switching over when you go to the track.