I was an active IMAC flier here in México til last year when problems occured and IMAC tournaments became extinct (for now at least). A friend had a GP Ultimate powered by an OS 46FX. It would never perform the most basic pattern. He changed for the OS 70 FS. It's vertical performance got better, but still far, far away from unlimited vertical (I'm flying over 8000 ft. over sea level). I dunno how it would perform at sea level, but I agree I wouldn't put a 90 on this plane...
If still willing to own a good aerobat go for the CG Ultimate.