This was interesting from this thread
IIRC the faster the cadence the less you pull up.
eg.
Stood up sprinting you pull up quite a bit. Which is where SPD's win.
Sat down your somehwere in between, your just about unweighting your leg, SPD's are of some but marginal benifit here.
Spinning at 120rpm+ most subjects were still pushing down well into the upstroke (i.e. past BDC), the downward force on the pedal was greater than what youd expect from just accelerating the weight of the leg.
So as most of you roadies sit down & spin fast, why not try a flat pedal that gets your foot closer to the axis of the axle, like the crampons (8mm)
Do any of the roadie pedals get your foot as low down as that?