I have mentioned before that I have ended up with some 175mm cranks, I usually run 170s.
I have been told that I could suffer if I use them, but I can't get to grips with the issue of the extra 5mm.
My saddle has been adjusted to the right height with the 175s so surely only half or less of my pedal stroke will be affected as at the bottom it'll be the same 34.5" in ma case.
Couldn't cleat adjustment have the same effect on knees during the forward stroke of the crank i.e moving my foot fore or aft would have the same effect either reducing or enlarging the circle my knees traveled.
That said I'm after some 170s to replace it.
I run 165 on my road bike and got 170 no the MTB, i will be changing the chainset in the summer and go for 165mm.
But then im only 5'7" and ride a 16" frame.
Shorter the better on the mtb, less chance of hitting rocks and roots.