Treechunk: do you move your foot around during pedaling? Like, in every revolution?
I have never been able to understand why tf people are infatuated with float. I mean, if you set it up correctly in the first place, you don't need float. Well, I don't, anyway.

So, OP: no, SPDs are not bad for your knees. 5° float is enough if you set it up properly.