Over controling the pitch refers to the amount of elevator travel relative to the stick input applied by you on the transmitter. If you have too much elevator travel(throw) the model will become very pitch sensitive, being easily over controlled. For general flying, where smoothness is desired, you don't need very much throw at all. On a 40 sized model it's not unusual to see no more than 3/8" or less for good control and responsiveness. For 3D flying you generally need all that you can get but that comes with some caveates. If you want to be able to fly that model in a 3D style your going to have to make sure that the whole plane is set up correctly as I described earlier. Basically what I am saying is that it takes more than a biger engine and a lot of throw to get a plane to fly 3D without it being a handful and nearly impossible to fly once you flip into high rates. Caps are known for being "snappy" and can get you inot trouble in a hurry if your not ready for it, making the plane heavier will only make these characteristics worse in most circumstances.

What you described earlier is a classic symptom of a set up that has far too much elevator throw. When I set up a plane one of the first things I do is check for any snapping tendancies. The test is simple, full power with wings level, pull hard and observe. If the plane does any weird gyrations I take out some throw and try agian. I keep doing this until I have found the point at which the plane only does a loop and suffers no departures. You need to do this both upright and inverted because the settings are often different. Once all of that is done you can fly with confidence in low rates and the plane becomes much more manageable in general. 3D is typically done either in the vertical or while flying slow so the rules change and you can use the higher throws that your high rates provide.