well the most powerful Amiga beyond the A500 without a doubt has to be the AmigaOne XE!! :-D
only issue is I dont know if the PCI card with the AGA chips on it ( to play old games 8-) ) is still going to be released.
having said that this is the eXtrEEm PoWeR Amiga to play games on but I mean the sort of games you et at LAN parties not games like Lotus3, thrust master, or Lemmings ;-) :-(
the price at this stage means you'd need to be pritty serious about your amigas so a base A1200 might be a good place to start these can be had for about $100AUD ($50USD?) second hand
