RE: Sig Somethin Extra VS Four Star
If you are comfortable with the 4-star, the SSE might just be a great choice. I've personally owned the ARF and built a kit version. Both are excellent.
The SSE is a mid-wing airplane and therefore doesn't have any dihedral. I've heard others say that the SSE doesn't knife-edge well but both of mine had no trouble. You just need plenty of airspeed. The SSE, like the Twist in your other post, is very nimble. Use low rates for the first few flights just to be safe. Once you are comfortable, turn it loose and have fun.