Best card to run in a x16 slot in x4 mode? No dual 8x on this mobo

Can I Connect a x4 PCIe board into an x16 PCIe Slot? - NI x4 slot Two of the world's fastest slots One delivers up to PCIe Gen3 x4 32Gbs transfer speed, the other one supports SATA3 6Gbs mode *Please refer to the x4d slot Storage options are plentiful as well, with dual 2280 slots One slot utilizes a PCIe x4 interface for blazing-fast storage speeds,

slot ad PCIe x4 speed vs x8 speed vs x16 speed Tested with rtx 3060 ti