Honestly, I'm not sure it would be worth it. It is often said you need a 10% difference in performance to even NOTICE a difference. Now, if you go from that 1900 to a 2400, its only like a 12% difference in pure clock speed (i think, correct me if im wrong). And, processors dont scale absolutely directly, so the performance difference might not even be 10%. But even if it was, is a 10% diff worth 379 pounds? I dont think so. Even if you overclock, i dont think the performance delta will be huge. My general rule of thumb is to never upgrade within the same architecture, unless you can double your clockspeed or something like that. The simple fact is, you probably wont see much difference. However, if you get the next newest greatest architecture, you probably WILL notice a difference.
But thats just me, hope it made sense
Butch
EDIT: Saw that you have waterkewling. Even so, i stick to my original post. Could you use the mobo you have now? If you just switched out cpus, it *might* be worth it. But then again, i still think its a good idea to wait for a new architecture!