Switch to 2X Xeon 5680 6-core, Will this work?

Nehalem was a huge step forward, due to the simultaneous improvement in both the cores and the system architecture.

Westmere has neither the luxury of improving system architecture, nor changing the underlying microarchitecture.
Within those constraints though, Westmere is a solid improvement for multithreaded workloads.
Two extra cores seem to yield roughly 20-40% performance improvements at the same power level as the previous generation.
For embarrassingly parallel workloads, such as those that GPUs excel at, the gains are likely to be higher - approaching 50%.

As expected, the single threaded performance for Westmere is almost identical to Nehalem.
However, the *multi-threaded performance increases by 42%* for the extra 2 cores.
Not perfect scaling, but pretty good.

Realworldtech

Westmere also has a new technique for detecting when the PAUSE instruction is used in a spin loop in a guest process.
When a spin loop is detected, the VM may deschedule the guest process to avoid wasting cycles that would otherwise be spent in the spin loop.
The PAUSE instruction is used for other beneficial purposes (e.g. temporarily pausing while an I/O is initiated) and not just spin loops.
So the detection mechanism must avoid triggering false positives, which could impact performance.
http://www.realworldtech.com/page.cfm?ArticleID=RWT031710140138

some workloads simply won't benefit from these new Xeons, because they're generally no faster in single-threaded tasks than the Nehalems that preceded them—and because not all server-class workloads these days are meaningfully compute-bound. Those are two very different sides of the same coin, but this is where progress to date has taken us.

In our view, the combination of the Xeon L5640 processors and the Willowbrook server may be the finest 2P server platform Intel—or anyone else—has produced to date. This setup's all-around performance is superior to the flagship 95W Nehalem, the Xeon X5570, which it shadows in single-threaded tests thanks to the L5640's generous Turbo Boost peak and conquers in multi-threaded workloads due to 50% more cores and cache. Yet the L5640's TDP is 35W below the X5570's, and its real-world power draw aboard the Willowbrook motherboard is marvelously minuscule.

http://techreport.com/articles.x/19196/10