NVME M2 drives: which slot to use?

I'm upgrading one of the 1TB drives to a 2TB I will use the MSI Expander on my Creator X299 motherboard to install the new drive so I can

NVMe SSD 50% slower on socket 1

m2 slot Two types of PCIe slot on an Asus H81M-K motherboard On the contrary, the L-series among others can only support cards using the PCIe standard in the WWAN

m2 sata slot GIGABYTE B460M D3H DDR4 Micro ATX Motherboard with Dual Nvme Pcie Gen3 X4 Slots, Alc1200 Audio Design, 4 Display Interfaces Support,Dual Bios