The i7-920 I have is a 4-core, 8HT 2.6GHz, and X5670 is a 6-core, 12HT 2.93GHz, but they are otherwise almost identical in terms of architecture. The Westmere is just a die shrink of Nehalem mostly. Aside from 15% CPU boost (which is really just a more stable silicon part running faster) the significant improvement from the Xeon is the extra 2 cores. (4HT)
For titles that are optimized for multi-core PCs, the point is, 3GHz*12 = 36GHz, which is *almost* as good as what you get with a i7-5820, which would cost over $350. Yes, Haswell-E is a more efficient architecture, but it also requires a MB+RAM upgrade. If you happen to have a Westmere-compatible board, the Xeon is a totally valid and much cheaper upgrade path, and until Intel gets their head out of their collective butt and stops charging > $1000 for an 8-core machine, a 2010 CPU will continue to remain relevant.
I mostly bring this up to address the "OMG YOUR CPU IS TOO OLD" comments. It's simply not true. Processors are only improving incrementally year on year these days.
(It is true that starting with Sandybridge, Xeons are nerfed because they can't be overclocked, but that's yet another reason the Westmere remains relevant)