Back on fitting for spinning. If your "knee over spindle" measurement has the knee too far back from the pedal spindle, you'll make it very difficult to spin fast. I have to have mine less than 1 cm and preferably closer to the knee directly over the pedal spindle.
I move back and forth in the saddle a lot, so I have to have the saddle far enough forward to keep my knee 1 cm aft or less during my saddle excursions.
Fore and aft saddle position is very important. You'll find that in the literature and I've found it to be accurate for me at least.
Al