x870e Taichi PCIe Slot Bifurcation

I haven't actually started to use my x870e Taichi MOBO yet other than to do a quickie franken-monster out of the case bench test on my desk to make sure it could POST (it did YAY!) since I'm still working on a custom made case for it (what can I say? I'm a slow flatulent geriatric).

According to the block diagram The top PCIe slot is x16 when the second slot is empty. When something is plugged into the second slot, the allocation becomes x8/x8. However, in the x870e Taichi Software_Bios setup Guide_English, on page 67 under Advanced in the BIOS (UEFI), AMD Platform Module, it shows:

PCIe/GFX Lanes Configuration

Allows you to configure J10 Slot PCIe Lanes.

Configuration options: [Auto] [x8x8] [x8x4x4] [x4x4x4x4]

Which one is the J10 Slot? Ideally, I would like to be able to run x8 with the graphics card in the top slot (that's all it needs) and X4,X4 in the second slot for a dual SSD card (it requires MOBO bifurcation). Is this possible?

Also, just below it, is this:

PCIe x16 Link Speed

Allows you to configure PCIe X16 Link Speed.

Configuration options: [Auto] [Gen1]-[Gen5]

Is this only for the top slot when the second slot is empty? I would like to be able to run the top slot at Gen 4 speeds and the second slot at Gen 3 speeds if possible (I was under the impression only the first M.2 slot could run at Gen 5 speeds).

The board only has two PCIe slots, so I assume x8x4x4 will give you what you want (top slot at x8 and bottom slot at x4x4).