In our testing, enabling Hyper-Threading on a Pentium 4 processor has generally resulted in lower performance in Content Creation Winstone tests. I wondered if this performance hit might be associated with Windows XP's mishandling of the UnmapViewOfFile function, so I ran some tests. Unfortunately, the results aren't encouraging. Microsoft's Q815227 hot fix for Windows XP doesn't improve Hyper-Threading performance in the Content Creation Winstones, and it actually slows Hyper-Threading performance in the Business Winstone tests.
Because of the way Hyper-Threading works, which Damage detailed in his Pentium 4 3.06GHz review, it's likely that resource sharing issues are to blame for any performance hit in Content Creation Winstone. If only there were a hot fix for that.