Main drive going in M.2_1, obviously. But I am confused in _2 or _3 is better for my 2nd drive.... It's a 2TB 970 EVO._2 supports PCIE 3.0 x 4 mode and M key_3 supports PCIE 4.0 x 4 and Sata mode MkeyI think whats confusing me is that _3 is 4.0 and _...