Dell Dimension 9150 Processor Upgrade

Hi!

I own a Dell Dimension 9150 and it has a Pentium D processor, 2.8Ghz.

Dell.com support lists: Processor, 80547, PENTIUM D SMITHFIELD FOR DESKTOPS..., 820 SKT-T, Male

What is the highest and/or best upgrade remaining for the Pentium D processors?

Where are some of the best places to shop at a relatively afforded price besides eBay??

I've read so many messages but still confused.

Found out that it may be Pentium D 840, 3.2GGhz but noticed that some people state that there are higher processors available such as Pentium D 930, 945 or 950.

Intel's website is Very confusing as it doesn't necessarily list the most meaningful info and there's variations within each processor class.

I plan to keep (hopefully!) the computer for another 1-3 yrs (?), have upgraded storage to 2 1TB HDDs, maxed out memory to 4G (though WinXp will only recognize 3..5G) and still has 370W PSU with Graphics card, 256, Radeon, X600 MRMGA+.

Would like to upgrade processor for video work that I perform.

Did not notice a sink fan on top of processor but will verify! Will I need one? Any particular thermal glue to help??

Any suggestions would be greatly appreciated.

Thank you!