I've thrown quite a few machine parts away, because I could be arsed selling them. And to be fair an 850Mhz isnt that bad really. But when you can but a processor for £40 that is far quicker, what could you get for an old chip like that.
When i say old, I mean in my terms, not yours.
As for your systems, The hyperthreading does make a lot of difference as does the FSB. a 3Ghz P4 533 Bus is about the same speed as an 800Mhz bus working at 2.35Mhz (when tested).
Memory is a KEY factor, as soon as your machine has to swap page files, it doesn't matter what processor you have, the whole thing slows dramatically.