I fly .60 size models on the S3004 servos. I do like the HiTec 605BB High Torque (now HiTec HS 635 HB) for the rudder, even on .40 size taildragers. You definately want a "tougher" servo if it is a single aileron servo.

I'm liking the Futaba S3152 servo on bigger birds.

And I use S3004 servos on throttles up into the large gas engine models. No sense hooking up a big $ servo for a little job.