bike fit and injury

Knee and hip flexion can be affected by the crank arms, which may lead to injuries down the road. Shorter riders using long crank arms may feel discomfort at the top of the pedal stroke even though all other fit measurements are correct.

I am 6'1" and can use 170's, 172.5's, and 175's quite comfortably.

Your crank arm length should be matched to your leg length.

Based on height a 180mm or 185mm is a 'suggested' length for riders over 6'4". In the end it is up to the rider for the fit, cadence, and leverage they want to get out of the crank arms.

Your picture from what I see is that your extended (locked) leg, with the crank arm inline with the seat tube allows your heel to lower a minimum of 20mm (.78 inches). Which is good because you avoid hyper extending your knees.

edit: if you are not purposely extending your leg...you need to refit for a slight knee bend. Then again we do not have the best side shot either.

I'm not a fit expert, but your leg looks like it's extended way too much.  The picture is at a bad angle so it's hard to tell, but you should have a little bend left in your leg when it's at the bottom of the stroke.  Have you had a professional fit done?

Your seat is too high!!!  (trying to make this place feel a bit like ST)