Actually, at 200 MHz in older versions, relatively stressful games (e.g. Sonic 3/Sonic and Knuckles, Ecco the Dolphin 2.. things that work the M68000 to over ~50% capacity most of the time) would run closer to 30-40 FPS. The application of the MMU hack by Squidge that accelerates ARM920T processor access to the upper 32MB of memory, where the framebuffer is located (and possibly some other bits DrMDx utilizes) is what caused the speedup of your average game from 30-40 to 59-60 FPS on average at 200 MHz. Now, there's practically nothing that overworks this emulator; though I do ask for an overclocking option to 300 MHz+ since my ARM920T makes it to 312 MHz with relative stability, and there are a few (extremely rare) parts of a couple games, like Globe Holder in Ecco 2 where the M68000 is running at near maximum capacity, the resolution is altered and intense graphical operations are transpiring, where you can see <45 FPS with 250 MHz ARM920T clockrate. But such events of course are few and far between.
I can't speak TOO much of MAME on the '2x since I only play one game in it, Aero Fighters. That game is pretty stressful; it has an M68000 and Z80 and some beefy audio hardware to emulater but with a small overclock runs remarkably well. Haven't tried Golden Axe, sorry.
