Rick, the Goldberg Ultimate flies fine with a 91 four-banger. I know of one with an OS 91 (not the Surpass, the original, which was not exactly a powerhouse), that does mild aerobatics quite well. You do want to keep it as light as possible, but that is true with any airplane. All this so-called "3D" business is fine for those who enjoy it, but the CG Ultimate is one of the best-flying models I've owned. I built the kit 12 years ago, with an OS 120, and am flying the ARF now with a Laser 150. Both are way over-powered at full throttle, for "normal" flying.

Just be sure to use two aileron servos. The kit provides hardware (bellcranks, etc.) for a single aileron servo driving four alierons. Not the best arrangement.