I need to run them using three risers, because I can only get two of the GPUs into the motherboard directly (I know for sure I don't need 5 risers and that I will be able to make the 5 cards fit in space with 2 on the mobo and 3 on risers).
My concern is as follows: There are only four 30A rails for the 6 PCI-E connectors:
The six connectors are on rails 12v3 (x2), 12v4 (x1), 12v5 (x2), and 12v6 (x1)
All of these are 30A rails.
So, Question 1: There are only four rails, so I would need to put 2x1080Ti on one of the rails. Can a single 12v, 30A rail power 2x1080Ti?
A possibly related Question 2: I will need to power the risers using the molex connectors, which only come from rails 12v4 and 12v6. But I can only put one 1080Ti on each of those rails, because there is only one PCIE connector for 12v4 and one for 12v6. This means I will need to power one riser using 12v4 or 12v6 but the card on that riser will come from either 12v3 or 12v5. Is mixing two rails together like this a bad idea?