I've been piecing together a maxed out Quicksilver G4 for old OS 9 apps and have been thinking about what the ultimate Mac would be for running apps that require a PowerPC. The latest version of OS X with Rosetta which allowed Intel Macs to run PowerPC apps was 10.6. I think that makes the graphics card the limitation. The best graphics card would be a 5870 (or flashed 6870?) or a Quadro 4000. So that would make the ultimate Mac Pro capable of running PowerPC apps: Mac Pro 5,1 (or firmware upgraded 4,1,) Dual 6-core 3.46 GHz W5690 CPUs 128 GB RAM (96 GB available in OS X) One of the graphics cards listed above SSD drive for OS and apps Large drive for data storage I'm considering building a scaled-back version of this but I also want to be able to boot into a more modern OS for daily use. I'd also like to have a better graphics card available for when I'm using a later OS, like a 680, 780, etc. I'd also like to only have one monitor connected. I would switch inputs when using 10.6 vs. the later OS. A x80 GTX could be installed in the bottom slot and use both 6-pin power cables. I assume it would be ignored by Snow Leopard. That would leave me with no remaining power cables and require the use of a GT 120 as the graphics card under 10.6. An alternative would be a lower-end card for OSs above 10.6. I've seen some 960 cards that only require one 6-pin connector. That would allow the Quadro 4000 to be used under 10.6. It only requires one 6-pin connector and only occupies one slot. If I were running Seirra (just an example but I know I want to be running at least 10.9), how would I get the OS to ignore the second graphics card (the one I was installing for use under 10.6)? Would setting it to just mirror the main desktop work? Note I have built Hackintoshes, but the idea behind a system like this would be to be able to get multiple versions of OS X up and running without problems.