Well, anyway, I’ll leave them in the recommended slots: 2+4.Performance isn't the issue, or in question here. It is purely a matter of avoiding configuration errors, instability, degraded signal integrity and trouble free operation in general without random and unexplained memory errors from signal disruptions. Has nothing whatsoever to do with benchmarks, FPS or any other performance indicator. And since not every board is identical, there are going to be differences in the level to which these factors might be present or non-existent. So while it's great that you are able to run a pair of sticks in both configurations without any obvious problems while running your synthetic benchmarks, it's really not an indicator of whether or not it might be given a specific workload or extended period of sustained usage. And to be honest, nothing you ran even includes anything I would recommend running when testing memory configurations anyhow.
Even so, a sample of one, as we well know, does not ever "tell the tale" anyhow.
Just for my curiousity, what benchmarking programs are you using?
Prime’95? MemTest? FutureMark? PCMark? Sandra?
If so, I also have those, but I didn’t wanted to waste too many hours on benchmarking. 😃