All other things being equal, you can generate more power sitting forward. The problem with this is trying to maintain this position and power output per stroke for hours on end. We need to sit back a bit to get the weight of our upper bodies off our hands, and pounding the pedals all day is hard on the knees and quads. Sitting back allows the back muscles to do more work supporting the upper body and brings the hamstrings into the pedal stroke.

I have long femurs, too, but frankly I have no idea where my kneecap is relative to the pedal spindle at 3 o'clock. I do know I can ride for hours without any kind of discomfort above the waist, and I can easily sit on the nose or get out of the saddle without throwing my balance off.