Been there, done that...

I understand your dilema all too well. Gas is so much better than glow for so many reasons it isnt funny, but unfortunately the best gassers are pretty darn big. If you're not into competition, I think you'll be very happy with any of the 80" kits out there right now, and there are a lot of 40-50cc engines to choose from, from BME to DA to Brison. The great thing about the 80"er is you can get away with a little less servo as the control surfaces arent much larger on a 28% than your 24-26% glow's. You *should* be fine with whatever you are using for ailerons and elevator now, the Rudder will probably be your only necessary upgrade - but without knowing specifically what you are running now, I cant say for sure.
If you're in competition, the picture changes - in that case, start saving for the hummer....


hope this helps.