GPsp in terms of emulation-achievement on the GP2x. The paradigm shift in terms of what was possible after it's release was probably analogous to the original release of Gigadrive, the first megadrive emu using cyclone.
In terms of sheer brute achievement, though? Personally, I'd go with M-HT's port of Albion - despite the lack of any source code whatsoever - by static recompilation. If you'd asked whether full speed genesis or GBA emualtion were possible prior to Cyclone or GPsp, the answer would have been "yes, but it would require someone to make an incredible effort, and the chances of that are unlikely". In my view, the chances of someone actually statically recompiling not only an x86 game, but one that needed a pretty darn good x86 at the time to get a decent speed, without source, would have been sufficiently unlikely just to answer "no".