For X9DR3-F can you tell me what cards can go into slot CPU2 Slot6 PCI-E 3.0 x16? It would seem that the location of P1 DIMM C1 limits the type of cards which can go in this slot. I suspect it must be half length card, however the website does not specify this.
Yes, slot6 supports up to 6.6” (half length cards)