Originally Posted by merlinextraligh

But IMHO, you're overthinking this anyway. Get a crank that fits your leg length biomechanically. Then worry about your gearing independently.

The change in "gain ratio" isn't going to be significant anyway. Using Sheldon Brown's own calculator, going from a 170mm cranks to 172.5mm the change in gain ratio is lost in the rounding, and going up 5mm from 170 to 175, makes a .03 differece. In other words it makes less difference than a change of one tooth on the cassette.