Lets say i got [link=http://www.hobbypeople.net/gallery/127505.asp]this[/link] plane, its a 15 sized plane, would a magnum RFS .30 be oversized for this.

Is not a 3D plane ; Small Elevator/Rudder/(can't see ailerons) for 3D maneuvers; Good for Pattern aerobatics only; 30 Size engine is excellent if this was a 3D capable plane. Good luck) ; Check and see if other's have any ideas making some modifications on this one to make it 3D capable.Good luck.

It would make a good chuck around for keepin in the back of the car, but the tail fin does look tiny. Maybe do a flip style rudder on it, and build some larger elevators and you should be fine.

PS, I like the statement half way down the tech spec,

Radio: 4 channel minimum with Y-harness or aileron servos. [&:]