The MDD machine I am typing on now is a dual 1.83 Ghz PowerPC, i bought as a stock upgrade. Boots Mac OS fine (the reason i got it) (9.2.2) . Uses both cpus in os9. i do not have proper cooling to play timing boost games.
Its a Encore MDD MDX Duet for xServe or MDD
Sadly I lose the third level of cache (L3 cache) with this card, but it has a much larger L2 cache so i do not miss Apple's L3 cache.
In all benchmarks I am more than pleased. It was a ton of money, but in a few months it might be impossible to find, as all things are if you wait forever. The other reason I did it was that I had only one CPU in this web browser/gaming machine. So for me the ton of money was worth it, because I need os 9.
I built a 4 cpu hackintosh for dirt cheap i use for development on (Apple requires x86 for iphone development, unless you use the third party non-apple iphone compiler and hacks) : Hackintosh = 10.5.2 = Kalyway + iATKOS
The engineer from Newer Technology that figured out how to put ANY cpu into almost every mac product on earth, left the business about 3 years back or so. That is one reason we have no G5s in our g3 and g4 machines. His name is Ben M. He works for the main competitor of Scientific Atlanta now doing all sorts of hacks for older cable boxes to squeeze new firmware code remotely into old existing boxes.