Wine is NOT an emulator. Hence, it is not any slower than windows. It runs everything just as good as windows. The only problem is that sometimes the drivers (for example, ATI is notorious for making shitty Linux drivers, while nvidia is a huge *nix fan) sometimes blog up the system and make it impossible to play, but all old games are completely playable.
There is also a program called cedega which is specifically designed to be a Windows API emultor for games. It's very nice and fast, however, it has bugs with some of the newer games, and generally takes about a year for a game to become 100% windows-like on linux.
Oh and all good game dedicated servers, be it UT, CS, BF, any of those games all versions, have far better Linux servers than windows.