The problem with the smaller servos in the bigger planes isn't the torque as much as the small motors. Your putting a strain on the motors so they won't last as long. I have used the HS 81s in small race planes ailerons with good luck, no failures to date but these planes only get flown once a month for three 8 lap races and they aren't moving the controls very far, just leaning the plane over a little. If room in your wings is a problem they do make tapered servos that are smaller just for that problem. You can look at servos on Tower or Servo City web sites to get an idea of what is out there in servo land.