Okay. I don't recommend a plane that's capable of 3D flight for a second plane. I know you're anxious to move up to aerobatics, but I'd recommend at least one intermediate step. (no one has any patience today. It's always gimme, gimme, I want it NOW!)

Anyway, I usually recommend a Great Planes Super Sportster a a second, providing you've really learned to fly your trainer. It's a good handling plane, and powered with a 46, can do most aerobatics albeit, in a smooth, pattern type flight as opposed to "stalled" 3D type. But it should be plenty to satisfy someone coming off a trainer. The 4 Star series is a good option too, as is the Kaos.

3D capable planes also have to be handled carefully. Do you have the discipline to NOT fly it at full throttle in level flight? One such flight can destroy the plane if you don't know what you're doing. (Those large control surfaces necessary for 3D are extremely prone to flutter.)

Now, poor 13 yearoldpilot has been hollering to be heard here for awhile, so I'll add a bit. The Somethin' Extra can be a relatively docile flyer if the rates are turned down low, and it's set up a bit nose heavy. With enough power, high throws and the CG set back, it capable of some pretty drastic manuevers, but NOT truly 3D capable. (Surfaces aren't large enough.)

Before you consider something more aerobatic than the above, I'd recommend getting real good with doing aerobatics with the trainer. (It's more capable than you may think.) Turn up the throws and learn to consistently fly inverted; do decent spins; fly knife edge as long as possible; Cubans and Immelmans, Split S's and stall turns; then get proficient at 4 point rolls and rolling circles.

IF, and that's a big if, you can do the above well, and without much thought, then I'd say maybe you could handle an Extra or a Giles 202.

Just my humble opinion.
Dennis-