In the past, with previous versions of DDR RAM, didn't the placement matter for performance? Technically it should still matter since the more RAM you use (slots), the more voltage your mobo needs & the more the memory controller has to switch to the correct RAM in those slots (more work), which makes it less efficient than using less RAM slots. But if you only use one stick of RAM (16GB), then you aren't utilizing the dual channel capability, so there should be a loss in performance. I'd rather have some benchmarks on this to be honest, but I haven't seen this tested anywhere.