Just a quick update. NUC5i5RYH is fully compatible with Samsung 850 EVO M.2 SSD. CrystalDisk speed benchmarks about 500MB/s read and write.
I was using "ZTC Armor 42mm M.2 128GB SSD (ZTC-SM201-128G)" with my NUC. Read speed reach 500MB/s but write speed just around 140MB/s.
Hope this help.