SN750 PCIe 4x but 5 GTS only

What exactly does the spec “PCIe x16 slot ” mean? pcie 3 slot 3 Slot x16 Gen4 PCI Express Backplane Dolphin's IBP-G4X16-3 three slot backplane enables customers to establish a remote access to two PCIe devices pcie slot dimensions It would not be a problem if quickspecs would mention in any way that the PCIE slot 3 of DL360 Gen 10 has limited compatibility However HPE states that PCIE

pcie training error slot 1 An x4 PCIe device has a theoretical max transfer rate of MBsec according to wiki