With Speedplay Zero pedals and Sidi shoes your metatarsal is only 8.5 millimeters above the pedal axle. That is less than half the distance with Shimano Shoes and Look pedals that are at 22mm. This results in over 50% less rocking torque. Even if you don't use Sidi (or Carnac) shoes your metatarsal is still only 11.5 mm above the pedal axle. The only brand that comes close is Time when used with their own brand shoe, and it still a minimum of 6.5 mm higher than the worst Speedplay Zero combination. Speedplay Zero pedals offer the lowest rocking torque and most direct power transfer of any pedal system by a substantial margin. You will go faster with the same energy using Speedplay Zeros.

http://www.bikesportmichigan.com/reviews/speed0.shtml

Rocking Torque:

I use Shimano Dura Ace SPD-R SL pedals and Shimano R150 shoes. Which shoes or pedals do have less rocking torque? Speedplay? Time?

But does somebody know it for clipless pedals?

I have found this:

Time Impact 7.7mm with Time Shoes
Speedplay Zero 8.5mm with Sidi Shoes

More info on "rocking torque" please. Does anyone have detailed info on this subject. It's hard to think changing pedal distances by a few mm is going to effect things that much... Can anyone quantify this ? Or is this just more marketing crap!

Remember when you were a kid and you had a tricycle with those red, wood pedal blocks on them so you could reach the pedals? When you pushed down hard on the pedals the darn things wanted to jump out from under your feet and spin around. Maybe you banged up your shins a couple times. That is rocking torque. The harder you pressed, the more the pedal wanted to dive out from under your feet.