Heres some benchmarking done by Toms Hardware
which should help you decide. It is quite the investment though, I'm in the same boat and cheaped out with a PentuimD upgrade which let me reuse my ram, drives, and agp Video card. I don't need bleeding edge hardware to play UO...LOL
By the way, you don't have an extreme edition processor - those all had 2Mb cache and you have 1Mb. You just have the Prescott core which is sometimes refered to as the E edition.
On a side note: Intel is getting ready to release the Quad Core Cpu'*.
if your really looking for some performance (read the artlicle, you'll be surprised at the overall performance increase)
98 SSEi 111,222 miles.
Intense PCM, LS6 Valve springs, PEMS, FWI. Hawk Street Pads.