Hyperthreading performance and game servers

I have a hard time finding some hard facts about it, and I can't really run any benchmarks myself, so I figured I'd ask here:

Can hyperthreading decrease performance on a machine that runs several single-th开发者_如何转开发readed CPU-heavy applications? In my case it's a Xeon Quad-core running about 6 game servers, 5 of which are on the Source engine.

My fellow community leader keeps insisting that disabling HT on the server would be beneficial to its performance. Does anyone have facts to confirm or dispel his claim?