HyperThreading (HT) on single core system?

[macbrush]

I was playing around with all the BIOS settings, and noticed that if I turn off HT in BIOS, it gives me 10% - 50% improvements on every test performed on xbench.

 

Maybe because Mac OS X was never meant for single core HT CPUs, so it is optimized for multi-core CPUs, and turning on HT on a single core system actually decrease the system's performance? Any thoughts on that?

 

CPU: P4 3GHz Northwood

Chipset: Intel 82865

OS: 1048 kernel 8.1.1

Memory: 4GB

 

Another thing, in System Profiler, the bus speed is reported as 400MHz. Is it the front side bus (which should be 800MHz) or just speed of memory bus?

 

Thanks