Can't do that on 1.25ghz-2ghz intel or amd pc, with winuae without lag city (at least for very demanding 68k games) but I don't know much about g4 or mac hardware in general.
Could you name "very demanding 68k games"?
What type of 1.25ghz-2ghz intel or amd pc?
Is it Intel Core 2 or Intel Pentium IV or Intel Atom?