ConnectX-3 are PCIe3 x4/x8 cards, even the SFP+ ones. The older connectx-2 cards are PCIe2. If you want to go all-out fast and not need a switch you can use a

ConnectX-3 are PCIe3 x4/x8 cards, even the SFP+ ones. The older connectx-2 cards are PCIe2. If you want to go all-out fast and not need a switch you can use a QSFP+ <-> 4xSFP+ cable or splitter by getting a QSFP+ card on the server end.