PCIe 2.0 sometimes faster than PCIe 3.0?
There were some instances in our testing as you saw where the PCIe 2.0 platform seemed to be a few percent faster than PCIe 3.0. There were a few cases of this in our testing. Some of the performance between 1-2% can be attributed to the margin of error we have talked about. However, there is another component to PCI Express besides just the raw bandwidth benefits of PCIe 3.0 versus PCIe 2.0. We are talking about latencies.
Just like your RAM modules, the PCI Express bus also has latencies and timings. As we all know, changing the timings/latencies on your RAM modules can affect the bandwidth or performance of your RAM. The tighter the timings, the better the performance. The same is true for PCI Express. It is possible that there are some timing or latency aspects that are different between the Sandy Bridge platform and motherboard we tested with versus our Ivy Bridge platform. This is just a theory of course, but without knowing the specific latencies and timings involved it is impossible to say for sure. It is a logical theory however that could account for a percent or two of performance differences experienced.
Think about it like this, in a bandwidth starved situation, PCIe 3.0 will more likely show a performance benefit over PCIe 2.0. However, when bandwidth is not starved, and not an issue, then aspects like timings and latencies play a role in performance. We may be seeing some of this where bandwidth isn't an issue. In most cases, it appeared that bandwidth was not a major issue in any of these games.
