Will my graphics card run at 8x if I install a 4x adapter for NVMe in the 8x slot

Solution
Yes.
PCIE x16 slot switches to x8 operation mode, if you put anything into second PCIE x8 slot.
Yes.
PCIE x16 slot switches to x8 operation mode, if you put anything into second PCIE x8 slot.
 
Solution