According to current tests, the sweet spot is 6400 MHz with the lowest possible CL. E.g. G.Skill Trident Z5 Royal Neo (2 x 16GB, 6400 MHz, DDR5-RAM, DIMM) . But also works well with 6000 Mhz. See: https://youtu.be/c6p92kme-1c?si=fyqYT6ZSc62_vqLW

We currently have no returns of these, only new goods. In general, however, we only resell mainboards if the cover is still present.

Yes, if you want to have 16 lanes for pci 1 gpu, you can only put a second m2 ssd in slot 3 or 4 without any loss.

Board only has dual channel memory, so 4 rigel should not bring any performance

If you haven't already done so, don't hesitate to contact our customer service department: https://www.digitec.ch/help

We should receive another delivery in about a week.