RE: Servo Selection
frabru,
I don't think the Super Sportster will be a killer 3-D machine, or are you planning on using it as one? If GP recommends the 9001 all around then any servo equal to, or better than, the 9001 should be fine. I think the very powerful servos are necessary for large, powerful (read: big gasser) 3-D machines with huge 3-D control surface movements.
There is a little factor of which you should be aware: Hitec recommends, when using karbonite-geared servos, to have one servo per surface per 12 pounds of airplane. You are real good on the elevators and perhaps marginal on the ailerons and rudder. However, the 635HB is so much more powerful than the 9001 you will not be loading it heavily at all. There is a Hitec Sub-Forum in this Forum. Perhaps you could ask the Hitec guy.
The Super Sportster is a nice looking airplane. Hope it works out well for you.