If you look on Ebay, or Craigslist you'l be paying retail. Try the local recyclers. They're common usually common there.
I haven't heard back from Susquehannock about the unlocked Xeon on his T5500. The RDIMMs might be an issue. I might go back to plan A with the known good T3500 for now.
I just ran through 20 pages of userbenchmark runs for the T5500 and didn't see a single W3000 series Xeon running. I did see X,W,E,L 5000 series running.
I GUESS IT'S TIME FOR THE DISCLAIMER. A LOT OF WHAT WE'RE DOING HERE IS EXPERIMENTAL IN NATURE. THAT MEANS IT MAY HAVE NEVER BEEN TRIED BEFORE AND WE DON'T KNOW IF IT WILL WORK OR NOT. OVERCLOCKING THE T5500 IS IN THAT CATEGORY. SO JUST BECAUSE YOU SEE US DISCUSSING SOMETHING HERE DOESN'T MEAN IT WORKS.
What is known to work is the Dell T3500 and any of the unlocked LGA1366 CPUs. Basically if the system will boot with an unlocked CPU Throttlestop should be able to overclock it.
On X58 systems all the CPUs run,i7, 3500,3600 series Xeons, 5500,5600 series. It looked like they were all interchangeable, but the dual CPU chipset may be more particular.