Sorry man i mean PCIe 3.0 x16 gpu on pcie x16 mbPCIe 3.0 is the generation technology of the PCIe interface.
PCIe x16 is the number of lanes the slot has.
They are not the same thing. So assuming you're just referring to having a PCIe GPU, in which case, you should be fine plugging it into the PCIe 3.0 x16 lane.