Well, just built a new system (the older's last choke was this test...), now I have a AMD 2600+ (real clock 2.083 Mhz), FSB333, memory bus 333 Mhz, and the old disks and peripherals and OS (with SP4).

Rendertime now is...210 secs!!!
I outperformed all the 2.8 CPUs minus one, and many P4 3.06!!!!!!!

Ok, the OS is clean now, but it isn't optimized yet; I have many tasks running, my systray is ten centimeters long :-DDD

I'm scratching my head trying to understand the means of that, I can only think about FSB and memory bus speed...
Time to try a clean render...stay tuned :)