I basically echo what Silver said..

One piece of advice.. when you make that change dont try putting gas on planes that are 72" wing span or most 1/4 scale planes. The wingloading just makes it go from flying to dropping in a click or two. When I started with gas ( Iwanted to really badly) I spent time and money trying to get too small of a plane fly with a gas engine. You need to find a very light engine to fly small planes on gas.

There are smaller planes that will fly well with a 25cc engine like the Brillelli www.brillelli.com but for 3d you need more power so it becomes a weight issue again. Try 27+% planes... or even the Great Plane Patty Wagstaff Extrta 300 will fly well on gas... it still floats well on landings and flys great with a 40 or 50cc.