Re: Windows 7 = Windows Vista Sp2?
Wine 1.1.5 was released recently and lots of people use it for games. World of Warcraft works, Guild Wars works as do a multitude of other games.
Do you lose some performance? Yes - i won't argue that, but when you are getting 150 frames per second anyway, why does it matter if you drop to 110? or 90? as long as it's more than 30, you're eyes dont know any better anyway. Also, there are zillions of free games for linux - mostly right in the package manager.
As for DX11, no it doesnt support that natively but Wine is a powerful tool. You can run anything for the most part. I have personally used DVDShrink, Guild Wars, Office 2003 and 2007, Crystal Reports, Google Chrome browser, C&C games...and there are whole websites dedicated to gaming in Linux.
EDIT : I am working on getting Microsoft Great Plains to run in Wine - and save for 2 dll's that wont register, it runs fine. Amazing stuff.