IME snappy planes have either too much elevator throw, the number one culprit IMO. If your loops are huge then you definately have something else going on and my next culprit would be the elevators are traveling unevenly. The ONLY way to veryify that they are in syc is to get a pair of clothes pins and CA some pushrod wire or coat hanger wire on them, about a foot long peice is usually sufficient. Clip the pins on the elevators and bring the tips of the wires close to each other and bend them till they are right next to each other. Now turn on the plane and move the elevators through their full range, the wire tips should track each other perfectly, if they don't your gonna have issues with the plane.

Next is the CG, I have found that NOSE heavy will result in a much more violent departure than a tail heavy condition will. My favorite method for checking balance is to roll inverted and let go of the sticks at about 3/4 throttle. If the nose drops and the plane heads for the ground at a steep angle your way nose heavy. If the plane climbs your way tail heavy. If the plane flies perfectly level(rare) your neutral. I prefer then to drop the nose just slightly, one or 2 clicks of down trim would get the flying a level track at the most.

After that if nothing seems to be helping you either have a model that has an incidence problem or one that is grossly over weight. Incidence is easy to check with a meter, if you really want to get it bang on(and this can make a HUGE difference in ALL of your models BTW) buy 2 meters and put one on the tail and one on the wing at the same time, compare readings between the two. Do the same on the wing panels and then on the same panel but one on the tip and the other on the root of the wing to check for warps.

Something I have done for quite a while is to set up my planes by first adjusting the radio sub trim to get the servo arms at 90 degrees to the servo case then adjust my linkages to obtain zero degrees of incidence on elevators and ailerons. You should also check up/down thrust at this time as well. After setting up the plane I fly it and usually there will only be a couple of clicks of trim required, if any at all.

Most of us tend to (eyeball) where the surfaces should rest while in the neutral position, especially the ailerons, which can result in a built-in couple of degrees of unintended posative or negative incidence. A couple of degrees doesn't sound like much but it can be the difference between a model that flies extremely well and one that has nothing but problems.

Just out of curiosity what is the span on your plane and what is the weight of the model with the tank dry?