There have been issues booting from PCIe M.2 SSD drives. Some motherboards support it, others don't.
The Samsung XP941 / SM951 do not have their own option ROM, so rely on the module being built into the host system / motherboard.
According to this page, the "AsRock Fatal1ty 970 Performance/3.1 works and boots with the SM951". It also says that a similar AsRock 970 motherboard "supports PCIe 2.0 x2", so you would probably be limited to 10Gbit/s as Dee has already mentioned.
The PCIe3 to M.2 adapter Dee posted a link to says "Samsung PCIe M.2 SSD doesnâ€™t support system boot". I would expect this to be motherboard dependant, but it is something to keep in mind if you go down that route.