Processor upgrade.

[Ait'al]

Does anyone know the best proccessor to upgrade for a 478. Is there a definite best 478? I was wondering if there were any good ones after the prescotts that were worth getting as a last upgrade for an old pre pci-e system? A new egg review from sometime back for a 3.0e, or 3.2, or something, said at some release was overclocking really high and it seemed like a good one to look into but I don't know if they are even available anymore. And it had some more upgrades on it than the first presscotts. I don't know which one it was though or what the upgrades were. I'm on the P4C800-E board from asus. It supports 400/533/800 mhz. I saw alot of stuff come out that was both 775 and 478 but I never knew if any would be better to get than the 3.2 or 3.4s that already existed or much about what changed since the pci-e came out. What new things should I look for for a last upgrade. I want to find the best. And is there anything worth getting as far as support beyondas mmx, sse, sse2, etc or what is best now to keep up with newer computers. I was wondering about new ones with higher caches but what do I want to look for in the new proccessors(the newer 478s). I've seen some with higher caches for the 478 but I don't know how far they went or if they are worth getting. I'm guessing there are quite a bit of changes that have been going on. I've also seen some that are smaller than the 90nm that I though were for the 478. Are those better now too. They all seem pretty ineteresting but I have no idea what I should go for.
And if anyone knows off the top of there heads what can the P4C800 go up to. And on top of it did any of them overclock well? Or is that worth anything?