Only some Intel CPUs are compatible with dual-socket motherboards.
You'd be much better off with a Core i7 CPU,
which has 4 cores + hyperthreading = 8 logical threads.
Moreover, triple-channel memory bandwidth STARTS at 25,000 MB/second
at stock settings, and goes up from there.
If you really need multiple sockets, the Xeon line is now
available with Core i7 architecture e.g. Xeon 5500 series:http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=40000727&Description=Xeon%20Nehalem&name=Processors%20-%20Servers