I've revisited quite a few of the emulators I discussed earlier in my Retrogaming and Beyond on Mac OS X - article on various intel macintoshes ranging from a +- 1.4Ghz Intel machine with Ati 3D accelerated graphics to a +- 2.8Ghz Intel machine with Ati 3D accelerated graphics. Just to see if those new Mac's are up to the challenge (two Powerbooks, a macmini core solo and mini core duo, an acertosh and asustosh)

Richard Bannister's emulators just run fine as most of them are both intel/ppc binaries. As for the emulators that only have PPC based binaries, quite a few of the sub-16 bit system- emulators running in PPC code are running at decent speeds on 1.4-2.8Ghz Intels. But that does change when I tried running MacMAME. This emulator only seems to be provided in PPC binary format. The version I've tried is 1.03u2 with the Aqua interface. On the low-end Intels MacMAME runs ok in the 8-bit arcade machine-modes. Running MacMAME on the high end Intel 8-bit arcade machine-modes run fine but with the 16-bit arcade machine-modes (like NeoGeo) MacMAME just isn't able to provide a satisfying game experience. The sound is good but the frame-rate is varying. A completely different experience is to be had when you run the same binary on a G4 at 1.2Ghz also with 3D Ati accelerated GFX card - on that machine the PPC MacMAME performs very good and smooth on most arcade machines being emulated.

For now I say that a PPC based Macintosh will provide you the most solid Arcade Emulation experience. But with Richard Bannister emulators there is no real difference on what OSX platform you are as both platforms provide a very comparable experience.

I am curious as to why no one has created a native Intel binary, as the Rosetta emulation layer on intel OSX does provide a huge bottleneck. I am off searching for an Intel OSX MacMAME binary....
Some links to sites disussing the MacMAME-PPC-only dilemma:
Ars Technica users discussing the subject

Oh and a little surfing there it is, the promise of an Intel MacMAME binary