Oops, my bad! Yes I meant 5,6,7, it is the same with the WRX80 versions also.
Also, the C-Payne PCIe switch I mentioned earlier has an issue with ADA-class NVidia GPUs presently: they are forced into PCIe Gen3. Christian tells me there is a fix on the way via a firmware update soon.
EDIT: The software fix did it, now I can do better than x8/x8 and get full x16/x16 gen4 on x16 gen5 with no bifurcation.
That still works to bypass bifurcation: Gen3 x16 = Gen4 x8, which is what the bifurcation would do on a Gen4 platform at least. The fix would be needed to take advantage of Gen4 x16 on Gen5 platforms.