Personally if i were you, i would run and get a 3.4ghz Prescott. My friend has the socket 478 3.0ghz Prescott, and my other friend has the 478 3.2ghz Prescott. With socket 478, you dont want anything under 3.2ghz. But you have 300$, you can be picky.
It would be fairly simple to get that 3.4ghz running at 3.7ghz. After that, i would imagine some type of cooling system would help. Every OC review i have read, or people i have talket to. Can hit 3.8ghz with a moderate cooling system fairly easy.
So i would get that 3.4ghz prescott, and save the RAM for another day. Becasue you can get 300mhz from that cpu with normal RAM. That should be a good enough increase intil you can afford some serious OC RAM.
Finished With TF.