As I said, DDR4 memory IC chips are heavily binned into different speed/timing tiers. Chances are you will never be able to get your kit to be stable at 2800/3000/3200. From what I have gathered from you I would say 2666 with tight timing will be your best bet. RAM vendors charge a premium for high speed high density RAM for a reason. @cadaveca has tested tons of RAM kits he may have better knowledge on memory IC chip quality. Also this means potentially your 5820K's IMC may be stronger than expected. If you pair your 5820K with some good quality DDR4-3200 14-14-14-34 kits it may just work right out of the box.