A point of consideration is that if you increase crank length, and drop your saddle to keep your knee angle at extension the same, you will end up with a smaller knee angle at the top. This adds shearing forces to the knee, and can add to the dead spot at the top of the stroke.

Personally, I am 6'1" and anything over 172.5 just kinda bugs me. But then, I am a higher-cadence guy.