There are over 1,900 games on Steam that run in Linux.
Sometimes I like to go back and play old stuff too.
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.
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.