Yes there is some headache in programming and matching up a pair of seperate servos. Speedwise, it is strictly servo dependent, extention length is a non-factor compared to the speed of the elctrical signal travelling it.

BUT...... You get one thing with the dual servos that I have come to really like, failsafe redundancy. If one servo or linkage fails, you can in all likelyhood limp the plane in. I have had an aileron servo fail on the left side of my stinger 120 but easily flew the plane in with just the right aileron working. I know size and weight are concerns, but if it fits, dual servos are cheap insurance.