In my opinion, the best gaming Amiga is an A1200. I've heard reports that A4000's are terrible for running games. A lot of stuff just doesnt want to run. It's best to have a hard drive (500mb should be ample really) and a little bit of extra memory (an extra 4mb of fast ram for example), just so you can load up your Terminal program and download games to your hard drive comfortably. (You'd use a nullmodem cable between the PC and the A1200). It takes about 15 minutes to send 1 disk though. Actually, you might not even need the additional memory, but when I tried to run hard drive installed games on my A600 awhile ago, I think most of them failed with only 2mb ram. (a1200 comes with 2mb as standard too).
If you want to play a few of the first person shooters, then an 030@50mhz accelerator will provide a nice experience without going all out for an 060 (which are more or less top of the line). And these 030's can usually be disabled on startup for games that choke on them.
