For me it's a Mac Pro and bootcamp, I've had great results.
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So, I've found that PC gaming is not insanely cheap. To get a good setup you're looking at at least $600. With a Mac, you're getting a Mac of course with OS X, and then with bootcamp you have a "traditional Windows PC" as well, to me it's two in one. Also, check out "Macvidcards" here on the forums and his huge selection of PC cards that work with OS X and will of course run under bootcamp. You can easily change the video cards every 3 years in a Mac Pro, plus it holds 4 hard drives. Sure the other machines don't have upgradeable video cards, so if you're that concerned go buy a PC. With thunderbolt though, I think that's changing.
Edit: yeah I know, "but the Mac Pro is soooooo expensive!!". Yes, it's not cheap for sure, if you NEED it for what you do, you'll justify the cost. You can also find the previous year pretty heavily discounted. In January of 2011, I bought my 2009 Mac Pro for $1699 from Mac Mall.
Also, I used to have a dedicated PC gaming setup. I loved it for awhile, for sure. I still very much enjoy building machines, but I had to consolidate. I found it hard to justify having a beastly Mac Pro sitting there and not using it for games in addition to video editing. If I can have one machine to do it all, then yes I'll do it. HOWEVER, having said all that...with the direction the new Mac Pro is going, when this machines time is up I'm going to build or buy a machine to replace it for editing and gaming, and probably just have a Mac laptop. Though this is years out. I'm running this Pro until it's little virtual wheels fall off.