Depends on how you plan to fly it.

Are you going to shoehorn a Saito 2.20 on the nose and fly it hard? I'd use 80-100oz servos.

If you're going to use a 120 size engine and putter around, the 60oz servos will probably be fine.

Actually the plane is fine with standard 40oz servos. But Sig RECOMMENDS 60oz servos on the flight control surfaces.

http://www3.towerhobbies.com/cgi-bin...&I=LXCXU0&P=ML