Crank arms will effect your comfort- typically knee pain if wrong, and your power. The crank length needs to match your legs. Pedal banging happens to the best of us, but its our own fault, need to time our power strokes a little better. Good luck- GREAT BIKE!!!
That’s what I have heard, thus far I haven’t had knee pains from the 170mm arms, and the 175mm arms on my rockhopper. I am about 5’11 just shy of 6.0 feet and am currently ridging a medium with the stumpy, and a large (which is a tad on the big side for me) with regards to my rockhopper.