I use a grey keo cleat on the left and a red keo cleat on the right. The grey has much less float.

So yes, your knees/legs can hurt from too much float. A related thing to check is saddle height and leg length discrepancy. If your saddle is too low or one of your legs is longer than the other, you can get more motion on the longer leg assuming saddle height is set for the shorter leg. All this stuff (leg, knee, foot, etc) is connected to each other and it is very hard to evaluate things on a standalone component basis.