Go with a pair of X5680s or W3680s. You'll thank yourself later, especially with the W3680s which can OC in software(ThrottleStop) on Dell systems.
Nah I wont run dual cpu's of that generation on this next machine, it isn't worth the power consumption for a gaming machine that will be switched on several hours a day. I don't like to spend much money in general that's why I run all this old surplus hardware :0. I run a pair of L5640s in the machine I use all day, total system wattage out of the wall is 150 watts. It's a little bit laggy under big load compared to the X5687 (which uses 360 watts! idling..
![Frown :( :(](https://tpucdn.com/forums/data/assets/smilies/frown-v1.gif)
) but they still both perform well, I have Perc H700s in them both with Raid arrays and 48 gig of ram. The original plan for the latest T7500 was to gut it for spare parts and run a pair of E5 V3 Xeons on a X99 motherboard (bit of metalwork needed also), but before I do that I want to see how it goes with a single first. The 5520 chipset boards like the T5500 and T7500 can't run the W series cpus by the way. That's an advantage the T3500 has for a little gaming box, the W can't run much ram either so isn't suitable for a workstation even if it could run in a pair.
I've ordered a crossfire cable.. I guess I'll have to try and find a pair of cheap GPUs to try out crossfire now.