No matter which way you mix it w/ the 9C there is a servo lag. It really makes a difference in the pulls. The only workaround that got them at the same speed was to use a Pmix for each elevator half (the Ch2 slot on the receiver is then empty), then they were both sluggish.

Im using pretty fast servos (3421sa) and if the servo speed isnt as fast as the lag you may not noticed any problem.