CPU Tests
The CPU tests paint an interesting picture. That picture shows there's very little difference when losing the memory bandwidth from two of the four DIMMS that make up the quad-channel memory architecture.
It could be argued that the tests aren't fundamentally memory limited, but even so, losing half the bandwidth is of no major importance when the cores are stressed. The results are not surprising once the amount of on-chip cache, particularly for the Core i7-5960X, is taken into account.
