Instead of the Ailevator mix, I use a p-mix with channels 2 & 5 for elevators. The Futaba website has a FAQ that explaines how to do this. No lag between the servo halves and the deflection and speed are identical. If using 2 & 8 the lag will be more noticable. I don't think the speed of the servo is reduced, its just that the lag makes it appear slower.

Ryan