If you're looking to run Sandy Bridge-E chips in a dual socket board, you can't. Those CPUs do not support multi CPU configurations. The motherboard doesn't even factor into it, the feature is simply not supported outside the Xeon processors.
If you're looking to use LGA 2011 dual socket boards, that's the Xeon E5. The cheapest 8 core Xeon E5 is around $1100 dollars. Add the motherboard and you're at around $2700 without any other hardware.
To be blunt, it sounds to me like you've got more money than sense and just want the computer for bragging rights.
This would serve no purpose as a gaming computer. It would be an obscene waste of money.
What is the purpose of this machine? What are you going to use it for?
Believe it or not, some people (and practically all enterprises/industries) use computing for things *other* than gaming!
The high core count is good especially if you are running a number of virtual machines, as I do. I work in HPC, and like to make my own "virtual supercomputer" with serveral VMs. Also, for running several services at once, it's good to have the cores/threads. And for doing actual math/science computing, many apps take advantage of the multiple cores/threads (or one can just run many copies of the app at the same time).
True, this isn't a typical home use, but especially the VMs put a big demand on compute cores (and RAM). I also like to play with CPU/socket/core afinity (ability to keep a process pinned to one specific core, and not jump around), so I'd like to have more than one socket. But unfortunately, doesn't look like that's gonna happen if it's coming out of my pocketbook (and no, the extremely large computer/software company I work for is too cheap to provide me with my own rig -- I work from home -- and so far I have been using my *laptop* to do this stuff!)