most likely the mid-high end desktop PC's (like ones you build yourself, with proper components NOT put together by some commercial OEM) by next year will be able to pretty much get max FPS, maybe 2 years. It seems like there is enough processing power in the high end dual cores (Core 2, Athlon X2, FX), but nowadays the most a retail computer (best buy, future shop, staples, etc) has in it is like an e6300 with crap ram, or Geforce 7300's - things that might make a consumer with little knowledge think "ooo a core 2 duo with a Geforce), and - don't get me wrong, that's a decent combination ... but it's not the high end. They put those chips in to make money. Lots of people with high end systems, (Core 2's @3 ghz with Geforce 7800 or ATi X1800) probably experience 55-60 FPS in lots of tested games. You can buy a comp from aretailer for 2000 bucks and it might have even a pentium d in it. Well a PD for 2000 bucks is a complete rip.
to summarize, it's always best to do some research and know what you're putting in. anyways that's my rant - hoepfully not too far off topic (we are allowed to discuss hardware here?)