The only downside to short cranks is that you get used to that length, which is fine if all you ride is short cranks. But, if you have other bikes with longer cranks, going back and forth from short to long can by irksome. I'm 6'1" and I normally ride 167.5s on my track bike. Its all fine and dandy until I get out my road bike or ssmtb which both have 175s. 175s feel too long after riding my track bike around for weeks on end, and it effects my pedaling efficiency for a while, until I'm able to readjust. I would probably be better off just going with 170s on my track bike and 172.5s on my other bikes.