In terms of overall gaming performance, the Intel Xeon E5-2637 v3 is massively better than the AMD Opteron 4274 HE when it comes to running the latest games. This also means it will be less likely to bottleneck more powerful GPUs, allowing them to achieve more of their gaming performance potential.

The Xeon E5-2637 v3 was released over a year more recently than the Opteron 4274 HE, and so the Xeon E5-2637 v3 is likely to have better levels of support, and will be more optimized for running the latest games.

Both CPUs exhibit very powerful performance, so it probably isn't worth upgrading from one to the other, as both are capable of running even the most demanding games at the highest settings (assuming they are accompanied by equivalently powerful GPUs).

The Opteron 4274 HE has 2 more cores than the Xeon E5-2637 v3. 8 cores is probably excessive if you mean to just run the latest games, as games are not yet able to harness this many cores. The cores in the Xeon E5-2637 v3 is more than enough for gaming purposes. However, if you intend on running a server with the Opteron 4274 HE, it would seem to be a decent choice.

More important for gaming than the number of cores and threads is the clock rate. Problematically, unless the two CPUs are from the same family, this can only serve as a general guide and nothing like an exact comparison, because the clock cycles per instruction (CPI) will vary so much.

The Xeon E5-2637 v3 and Opteron 4274 HE are not from the same family of CPUs, so their clock speeds are by no means directly comparable. Bear in mind, then, that while the Xeon E5-2637 v3 has a 1 GHz faster frequency, this is not always an indicator that it will be superior in performance, despite frequency being crucial when trying to avoid GPU bottlenecking. In this case, however, the difference is probably a good indicator that the Opteron 4274 HE is superior.

Aside from the clock rate, the next-most important CPU features for PC game performance are L2 and L3 cache size. Faster than RAM, the more cache available, the more data that can be stored for lightning-fast retrieval. L1 Cache is not usually an issue anymore for gaming, with most high-end CPUs eking out about the same L1 performance, and L2 is more important than L3 - but L3 is still important if you want to reach the highest levels of performance. Bear in mind that although it is better to have a larger cache, the larger it is, the higher the latency, so a balance has to be struck.

The Xeon E5-2637 v3 has a 536 KB bigger L2 cache than the Opteron 4274 HE, which means that it, at worst, wins out in this area, and at best, will provide superior gaming performance and will work much better with high-end graphics cards.

The maximum Thermal Design Power is the power in Watts that the CPU will consume in the worst case scenario. The lithography is the semiconductor manufacturing technology being used to create the CPU - the smaller this is, the more transistors that can be fit into the CPU, and the closer the connections. For both the lithography and the TDP, it is the lower the better, because a lower number means a lower amount of power is necessary to run the CPU, and consequently a lower amount of heat is produced.

The Opteron 4274 HE has a 70 Watt lower Maximum TDP than the Xeon E5-2637 v3. However, the Xeon E5-2637 v3 was created with a 10 nm smaller manufacturing technology. Overall, by taking both into account, the Opteron 4274 HE is likely the CPU with the lower heat production and power requirements, by quite a wide margin.