Best Memory spec for this rig?

hi guys
some of you that are good at buildups - I need to know what my choices are for memory, and in fact whether one spec is really better than another.
The model is a HP Compaq DC5800 with E8400 C2D running nominal 3.0Ghz, FSB 1333MHz. its the same electrically as the HP DC7800 but I think the motherboard part num is different for the two.

This model is hard to search in engines such as Kingston and Crucial have, because the same model Number can refer to a very wide range of components from Celeron to Pentium models, to Pentium D to the more numerous C2D's.

the original notes from HP [before a string of bios upgrades] stated either PC2-5300 or PC2-6400. Webbing around, I find a lot of people chose PC2-10600 instead.

I'd like to bump it to 4x2GB; I'm running Win7 Ultimate x64 and dropping a Radeon 6-series low profile pci-e x16 card in. It will do HTPC duties and lab mule/fileserve/etc

thanks for your advice