The problem with retro PPC or 68k macs is that the experience doesn't match amiga. I ususally find myself having to go up one generation on hardware and down one generation on software:
For example:
A PPC 8500 with 128 megs running 8.1 and Photoshop 4 is nice. Marathon plays nice, dark forces. But an Amiga with a GFX card is better in my opinion. With an 060 and Fusion Mac I was really impressed with the functionality of a 128 meg Phase 5 060 card. Switching back and forth using CGFX was great. Really impressed PC and Mac afficionados up till 1999 with this setup.
I recently took the 8500 apart as it was totally worthless.