Thanks!
This MB I’m planning to get (MSI X570 Plus) has a 1xPCIe 3.0 M.2 and 1xPCIe 4.0 M.2 slots.
My current set up uses a (5 year old!) 500gb M.2 drive for the boot drive. Are you suggesting I should put that one in the PCIe 3.0 slot and then look to get a dedicated flight sim PCIe 4.0 M.2 drive?