The best is normally the one with the highest number.
You're determined to upgrade regardless, aren't you?
If so, I'd get the 5200+ from the list I posted earlier.
This one for a more direct link.
How much RAM does your system have, as you'll probably notice more of a performance bump if you upgrade that?
//edit: The CPU with the most chance of being compatible is the 4200+ X2 on that list you linked to. Ebuyer also have the
4000+ X2 for £35. Both actually have a slower clockspeed than your current CPU though, so only multithreaded applications would gain anything.
Edited 1 time(s). Last edit at 08/04/2009 05:51PM by gav.