Taking into account the basic premise that these processors/platforms are not designed per se for gaming purposes, and without knowing if you can source these parts for an interesting price, let’s answer your question as well as I can. Intel Xeon CPU
For gaming, you want/need the fastest single thread/core CPU, and here the E5–1620v2 is the winner, at 3.9 GHz (one core) versus 3.4 GHz (one core) on the E5–2650v2. Even in multithreaded scenarios, where 2 (or more) cores are used (and you’ll find these in newer games), the E5–1620v2 is faster than the E5–2650v2 (3.9 GHz all cores vs. 3.0 GHz all cores).
If you want a more exhaustive comparison between these two processors, take a look at this CPU-Monkey comparison, where you’ll see how these two processors compare.
Anyway, if you plan on buying these processors, take into account that this platform (LGA 2011) is not cheap, and you’ll want quad-channel memory with any of these processors to take full advantage of them… but if you can get these for an interesting price, go ahead as you’ll have an interesting computer for many other tasks apart from gaming. Intel Xeon E5-2650 v3