Westmere overclockability?

I'm planning on building an SR-2 Classified system for folding@home work. I'm trying to find out how overclockable the Westmere Xeons are. I know with the i7 920/930/950 CPUs, you are going to top out around 3.8 - 4.2 Ghz folding stable.

The higher I can clock them, the more points I can get. But if the top end is only a few hundred Mhz between the cheapest and the most expensive, I'll be getting the $600 chips, not the $1700 ones.

I do know the L chips are 40-60W, the E are 80W, and the X are 95-130W.

Also, I'm probably looking at 3 months between buying the first CPU and the second.

Thanks!

Well, it looks like I could get the E5645 new for about $600 each from Newegg, but the multi is limited to x18 (x19 with turbo), which means I'd be at 200 bclock at 3.6Ghz.

The x5650 would give me a x20/x21 multi, and I think I've seen them used in the $500 range.