I am 6'5" with a 36” inseam.
I have tried 170, 172.5 and 175 on fixies. I do mostly open road riding with a little city riding. For me the 172.5, 175's work the best where I live. You can get up the hills easier and, most importantly, it is easier on the downhills. I have found you can descend steep grades easier with longer cranks because it is harder too wind out the rpm's.
I can get the 172.5 up to about 170+ rpm's on a few hills. The 175's would drop that to about 160-165 rpm's on the same hill, and I would lose some speed. I do not like spinning above 170 rpm's for too long, I do not find it comfortable.
The downside of the longer cranks are: I am very aware of my speed on tight turns. Fast downhills with blind turns scare the $**t out of me because of possible pedal strike.
I basically give up maneuverability to go up and down hills easier. That works for me.