Try UAE on an Athlon64 or a 3Ghz Pentium4... It's impossible to tell if you are running an emulator or a Real Amiga. Sprites are full speed.
That much is not needed. I am yet to see one single game not running at full speed here on my 2400XP+ Athlon.
With that said, I can also say that when I ran games on my old Compaq Presario at 350MHz I could not find a game that didn't in full speed. Did never try any demo or applications back then, though.
However, some chipsets seems to work very badly with WinUAE. I've got friends that have major slowdowns in games like Alien Breed 3D II. And, myself have yet to try out WinUAE on a computer where the graphics doesn't get completely trashed when moving the mouse when Workbench 3+ has loaded (this as long as one is running without the filters turned on and for some reason Workbench runs way much slower even with the simpliest filter turned on, very very strange).
But, like I said... not THAT much horsepower is needed to run most games fluently. As long as one remember to use VSync and some proper screenmode.
AGA emulation isn't perfect, though. Has anyone managed to get Brilliance up and running without any problems?