The MacPro is *not* a gaming platform, it's very disingenuous to compare that to a PC gaming rig. They're pretty much optimized to run image and video processing (AFAIK, I don't own anything of the sort), not do 3D graphics. Just so that it's clear to everyone, to compare you should check out the iMac:
http://store.apple.com/us_smb_78313/browse/home/shop_mac/family/imac/select?mco=MjIwNTQyNjE[url]http://store.apple.com/us_smb_78313/browse/home/shop_mac/family/imac/select?mco=MjIwNTQyNjE[/URL]
Now I'm not going to say it's better value for money than a PC, just a better comparison. There you'll get a quad i7 3.4GHz, 4GB RAM, a HD 6970M 2GB, and a very good 27 inch monitor for 2.3K.
Anyone got the links for how to put together a similar gaming PC? I'm looking to build a new one in, oh I dunno -- late August?

I believe it has been said earlier in this (stale old crufty) thread that a PC would be $1500 cheaper than a Mac, which should put such a PC plus such a monitor about 800 bucks...