raid – Asus Z170-A m2 SSD and pci-e lanes

I have an Asus Z170-A that is now a few years old. When I bought it I could only afford a combination of 250GB SATA SSD and 1TB HDD. My Steam games are on the hard drive.

With the fall in prices, I would like to upgrade storage to move my games to a combination of SSD drives. I could easily add a single SSD of m2, but I also started to see the possibility of a RAID 0 configuration using the dedicated m2 and also an empty PCIe slot.

Am I confused about PCIe lanes and will my board support two new SSDs in this configuration? I have a GTX 1070 to 16x and from what I can see, the Z170-A has 16 + 4 lanes. If I try to run a m2 at 4x and another in a PCIe slot at 4x, will I be in what is possible?