As far as I know, Hyperthreading is only useful for several applications running simultaniously within windows. But for games, which mostly need the full power of CPU and other ressources, hyperthreading can slow down the "application".

I remember buying a game (don't know if it was WoW or Battlefield 2) where the manual said, the user should disable Hyperthreading because of the above mentioned problem.

So I think, it's wether "your problem" nor a problem of your game.

Greetings,
Dirk