I play a lot of games and have never had an issue with SP2? It actually increases performance on most games and the few it decreases is hardly noticeable anyway! I'm sure i read somewhere online that it only decreases some games by a maximum of 3%! And this is only a very few games!
Admittingly I do have a 3.2ghz cpu hence why i dont notice any decreases anyway! I'm also sure one of the games its supposed to decrease performance by as much as the 3% on is UT2004 and I play that without noticing it. And Mafia plays fine.