Please can anyone help with this ?

I have had a Dell Dimension 5150 for a few years now and would like to upgrade the CPU if possible.
It currently has a Pentium D 3.0 ghz socket 775 LGA.

CPU-Z reports the following:

Intel Pentium D 930
Presler
Technology: 65nm
Core VID: 1.244 V
Bus Speed: 199.5 mhz
Rated FSB: 798 mhz
Mainboard model: 0HJ054
Chipset: i945P/PL/G/GZ

As I understand it, the motherboard will not take the modern Core 2 / Duo processors because of voltage irregularity.
I did read that it can take a Pentium 6xxx, though.

My question is, what would max out this machine: - a P4 670 3.8ghz or a Pentium D 960 at 3.6 ghz ?
Also, would i need to do anything more other than swap the processors ? For instance, new BIOS or altering any jumpers etc.

Thank you.