The .50 will be much nicer but your heli definetley has enough power to do inverted flight and loops. I am doing stationary consecutive flips, piro-flips, backward loops, and funnels, with a completely stock .39 helicopter. The advantage to learning 3D with a .30 is that it teaches you collective management instead of just powering through the maneuvers like you can with a .50. If you are confident enough to do loops and rolls you can go ahead
and move your ball links to the outer hole on the washout mixing arms so you will have a little more cyclic.