I can tell you one thing that will give you plenty of power on your CX2, but USE THIS AT YOUR OWN RISK. If you have a newer CX2 with the separate AR6100e Rx, you can try flying a 3S pack in your CX2. You get GOBS of power at the expense of the possibility of frying your 3-in-1 and overheating the motor. I have a FP 3S for my CX2 and she runs ballistic with that pack!

Having said that, it sound unusual that your CX2 can't lift the camera with a fresh pack. I would check for other mechanical problems as well as checking your blades, as has already been mentioned.