It all depends on what version pci-e slot, 1.0, 2.0, 3.0.
If a 2.0 slot has roughly twice the bandwidth of a 1.0 slot, then that would mean that a pci-e 2.0 at 4x would be roughly the same as a pci-e 1.0 at 8x.
So wouldn't that mean a pci-e 3.0 slot at 4x would be the same as a pci-e 1.0 at 16x?