Difference between PPC and Intel
If you happen to have generous parents that gave you a Mac mini for Christmas, then you've got a G4 mini. If you go out and buy one now, you'll get one based on an Intel Core. Does it make a difference?
I tried out all the emulators I have been using on a 1.66ghz Core Duo mini. All I can say is Apple did an amazing job on Rosetta. The emulators performed quite well. Pretty cool for what is essentially an emulator running under an emulator! In the case of SNES9x, a Universal binary is already available. Oddly enough though, the PPC version works slightly better. There was a slight video glitch on the Universal binary. I was able to get a full 60fps from the PPC SNES9x without noticing any glitches.
Most of Richard Bannister's emulator ports worked pretty good too. I was able to scale up the window and still get 60fps from several of them. Games were very playable. When I enabled some of the enhanced video modes performance started to drop. Richard Bannister is already working on Universal binaries and performance will improve considerably once they are released.
You're probably wondering why the emulators can't just be recompiled. It primarily has to do with the difference in proceessor architecture known as "endianness". Endianness describes the way numbers are stored, either forwards (2,221,181,105), or backwards (105,181,221,2).
Most of the time a program doesn't really care about endianness. In order to get fast emulated video there are a lot of bitwise operations being done. This requires making assumptions about where bits are stored in order to speed things up. In order to be converted from big endian to little endian a lot of calculations have to be redesigned. A lot of the emulators are already ports of code that was written for Intel x86 processors. In theory this should help speed up creation of Universal binaries if the code is generic enough and didn't make use of certain other PC architecture layouts.