Fast hardware are required for Windows 7 and MacOS X, it isn't necessary for AmigaOS 4 to feal good to use.
You can run windows 7 on the cheapest & slowest new hardware. I need fast hardware anyway, I would have no use for a slow PPC system.
The problem with AOS4 is that it isn't retro & it isn't modern. AROS falls into the same trap, however AROS is free and the hardware is cheap.