If you ride fast, the smaller total surface area will offer a slightly lower drag, and the smaller size of the wheel means the spokes are shorter, and thus catch less wind. Finally, the smaller size, all other things being equal, means a lower total weight for the wheel.

All of these factors should help raise the average speed, but if it's a factor in the real world, I don't know. 26" wheels should be at least as fast, anyway.