Try the Goldberg Cub .40 ARF . It lists the .91 four stroke as a possible candidate, and it should make a really nice airplane. Plenty of power(obviously), but with the right prop and good throttle management, it can still be flown in a scale-like manner.
http://www2.towerhobbies.com/cgi-bin...?&I=LXHEM1&P=0