Stack height DOES matter. Think of it this way. Pretend your foot is 12 inches above the pedal you are turning. I dont think anyone would be able to ride a bike very fast. As you applied power, your foot would rock back and forth as that power is being applied, and you would prabably rip apart any tendons or ligaments anywhere near your ankle.
Steve
www.sidemountpedal.com
sorry dev, i don’t agree. the efficiency of power transfer is not related to the distance between the sole of your foot and the pedal spindle. its related to the losses that occur during power transfer from the muscles to the pedal spindle. if you could bolt a human foot directly to the pedal, the distance between the foot sole and the spindle would not matter at all (other than via their effect on seat-2-spindle distance, which i am assuming are being compensated for with crank arm length and saddle adjustments).
alas (or rather, thankfully) you cannot do this, so the connection between the foot and the pedal will always have some amount of loss due to the lack of absolute rigidity in the connection. this comes from many sources, but none of them involve the stack height (certainly not in any direct way). if you increase the stack height in a way that increases force-induced motion in the connection, then sure, the new stack height sees lower efficiency, but its because of the motion, not the stack height itself.
i remember reading once that from a power transfer perspective the ideal pedal would actually be a spindle that passed through the ankle bone. no foot flexion, no foot collapse, no foot compression, no nothing. of course, comfort is compromised, as well as the ability to adapt to bumps and so forth 
Hi Vista,
What is the difference in stack between Look Keo and these pedals. How much are the pedals? Can they go in any crank or do they need a special crank. If they need a special crank what is the price and do they come in 110mm BCD?
Dev
Dev,
The pedals have an RRP of $299.95pr and can be used with any crank.
The chainrings are available in 110mm BCD.
Thanks.
Hey Dawhead, I think your analogy is flawed. In the ideal world, yes, the spindle would just pass through the ankle and you would stomp. No foot in there to mess anything up and add an additional joint and lever were losses occur…but as you add stack, you add another joint (vs having the mythical pedal spindle passing through your forefoot). I believe this pedal system effectively allows the pedal spindle to pass through your forefoot without drilling holes through your bones, virtually eliminating the ~2cm lever that adds no value but that is implicitly introduced by conventional pedal systems.
Dev
my whole point is that the N-cm stack introduces no leverage/motion of its own. the losses all come from the inevitably “imperfect” binding system. we can’t make a “perfect” binding system (bone bolts), so we have to compromise. but there is one and only 1 imperfect binding system no matter what the height actually is, so taking any given cleat system and increasing its stack height will not (for all binding systems i know of) change the efficiency of the linkage. when i talk about adding stack, i mean solid stack height, not just another look/time/spd layer.
to get this back to the original post, i can’t see any way that moving the relative position of the foot sole and the bolt center of the pedal can affect pedalling power transfer efficiency in any way assuming that the same cleat system is used.
In the ideal world, yes, the spindle would just pass through the ankle …
wow. your ideal world sounds nothing like my ideal world.