Hoping they are good. He's in the process of making my bike with 210 cranks.
Zinn has this adjustable crank he can put on a bike to help size you, I am 6'8" and it felt so good to test out a 208 crank. he uses all of your body dimensions to determine crankarm length, it seems natural if your leg is longer, why keep all of that leg coiled? On his custom frames with extra long cranks he raises the bottom branket to accomodate.
I am slobbering on this site every day until my bike is finished:
www.zinncycles.com
On the topic of knees, I have noticed some soreness in my knees with the current 170 cranks I am using. My leg is never extended and it is bent at more of an angle than I think is practical at the top of the stroke. but anyway.