I have a 33 inch inseam and ride 170, 172.5, and 175 cranks and spin like a gerbil on crack... The difference of 5 mm is really quite small and for average people this is a range that we can adjust to.

My mountain, touring, and one fg mountain bike have 175 cranks, road bikes are 170 or 172.5.

Maintaining spin off road is really crucial to maintain power to the back wheel, variations can cause stalls or spinning out on loose surfaces.

I ride a good number of fg bikes and find 165mm cranks to be a little short (longer femurs I guess) and am happy with 170 cranks and slightly narrower pedals or clipless to do increase cornering clearance.