Precision 670 CPU Support

I own a Dell Precision Workstation 670, which at the moment has 2 of the following CPUs:

"Nocona" (standard-voltage, 90 nm)
Xeon 3.0 1024 KB L2 Cache 800MHz FSB 1.287/1.4 V Socket 604

I would like to move on to something with a little more power, so my question is:

What is the most powerfull cpu supported by this computer? I have already upgraded the BIOS to the newest version. It seems to support dual-core XEONs, as evident in the bios (CPU Info -> Multicore capable: no in mz case). Most preferably, I would like to see a list of supported CPUs.

Best Regards