I have had 3 jets - 2 SpiderJets F-16 which were slightly overpowered with Simjet 3000 and controlled by tailerons only, and a small Sukhoi 27 with a Simjet 700. All of them fly/flew with Futaba S9451 servos (one F-16 was instantly rekitted, but not because of the servos!!), and I never had a glitch or a problem with control authority on any of my jets. I always like to use the same brand servos as receiver and transmitter, as they are made to the same specifications. Make sure that you get servos that can handle 6 volts.

Good luck!

Tor