HI Chris,
We found the over all best performance to be with a 1957 issue Fox 25 (the one built in the 19 case) since it has almost the power of a Fox 35 Stunt, but weights a little less and uses less fuel. Using just a clear finish on the wings and dope on the wood surfaces, Aaron kept his at 27 oz. RTF built "box stock". Built light, with a light engine, gives the best performance, like you say.
At the East Coast Oldie Goldies one year, 3 of the top 5 in Advanced Classic were Fancy Pants!