No body has ever been able to convince me that there is a mechanical advantage to 700c tires over 26" tires. Wheel diameter is just one part of the gear development formula with the gear ratio being the other part (the two are products of one another, they are multiplied together). With a constant gear ratio the larger diameter wheel will get you slightly further per pedal stroke but that disappears when you shift gears (change the gear ratio). With a slightly higher gear ratio you can still travel the same distance per pedal stroke of a 700C tire. I am not 100% sure about this but I think it is a wash. The higher gear ratio will require a slightly larger torque but the smaller diameter wheel will require a slightly smaller torque.