The manual lists the M2 slot as PCIe 3.0 x 4, so your speeds will be around  3500MB/s Seq. reads  – 3300MB/s Seq. writes. This will be dependent a bit on the brand/model # of the installed Nvme drive, but it should be able to get very close to it.
so I’m buying the new Alienware aurora r12 with nvme m.2 ssd. and when I research about the speed of the ssd (read and write) apparently no one is talking about it. so what is the read and write speed of the nvme m.2 ssd? also side question: is the ram good on the Alienware aurora r12. my setup is 3200mhz ram from Alienware  sorry of my bad english it’s my second language.  
Aurora R12, SSD speed