In this test, we had a very different result from when we tested the performance gain using dual-channel memory with an independent video card: using dual-channel memory on an integrated GPU provides a great performance improve in games.
The use of dual-channel memory made a big difference in those tests because the main RAM is used as video memory and, differently from the “real” video cards, the video memory is not exclusive. Using dual-channel memory configuration, and not single-channel, is like exchanging a video card with 64-bit memory bus for another one, with the same GPU but 128-bit bus. It is the same performance impact.
The difference is even bigger in games that make intensive use of both video card (by the GPU) and of the RAM (by the processor), since in this case both units must share the same bandwidth.
Another result we found is that the performance gain by using dual-channel memory was, in most cases, bigger on the A8-7670K than on the Core i7-5775C. A possible reason is the fact the GPU present on the Core i7-5775C has a 128 MiB embedded memory, which works as a memory cache for the video engine, thus reducing the impact of the smaller bandwidth of the single-channel configuration.
It is also necessary to keep in mind that our tests don’t make a direct comparison between the Radeon R7 GPU present on the A8-7670K and the Iris Pro 6200 present on the Core i7-5775C, since, beside the results are being influenced by the CPU power in each chip, other configurations (amount of memory and operating system) were not the same, since our objective was to measure the performance gain in two different situations. Besides that, the CPUs used in the tests have very different price tags, so it makes no sense on comparing both results.