3DMark05 - 22,359
Core 2 Quad Q6600 @ 4.0Ghz (445x9)EVGA GeForce 8800GTX 670/2250
3DMark06 - 15,158
Core 2 Quad Q6600 @ 4.0Ghz (445x9)2GB G.Skill DDRII800 1:1 890Mhz 4-4-3-5EVGA GeForce 8800GTX 670/2250
Do you plan on using a multi-gpu solution? If you do, then it will depend on whether or not you want SLI or Crossfire. If you aren't, then go witht he P35. The performance of both chipsets is about equal, but the P35 uses significantly less power and runs much cooler.
I'd go with the Q6600....expecially if you aren't paying for it. Single threaded apps will not see any benefit with an increase in core count. The only benefit you will see is if you are running a number of single threaded apps at once. The system will multitask with greater ease. Given that you are running virtual servers, I would expect that a quad core processor will really help system performance.
The only advantage of a dual core processor is they do tend to overclock better. With only 2 cores (compared to 4) they have a lower thermal output. This lower thermal output increases your chances of getting a higher overclock. This isn't always guaranteed. My highest clocking E6600 would run up to 3.8Ghz, while my current Q6600 isn't much further behind at 3.73Ghz.
What do you do with your computer? The best processor for the money is the Q6600 right now. They can run a bit warm overclocked, but you're water cooling loop should be able to keep the heat under control.