Wine is always a viable option, especially for older games. With DirectX 11 support coming later this year, almost every Windoze only game should hopefully work.
I do not see a performance penalty at all with WINE. Most games that work play at speeds matching or better than windows. WoW is usually a big example of that, as are emulators.
Running either in wine is a fine benchmark on performance.
Now, this isn't to say that Wine is totally up to par with Windows in terms of compatibility, but performance hasn't been a significant issue for quite some time.
This might be enough of a barrier to stop me using it right now.