2. I assume that in addition to latest bios, you also have all set of updated drivers for your NUC (chipset, rapid storage, management engine serial IO, etc...).
3. Are the benchmarks of your SSD correct and according to specifications?
4. What Operating System are you using? There are some problems with Sata 3 in Windows 7.
I am running W10 and all drivers are up to date.
I think it might have something to do with the Magician software as I checked the BIOS and the M.2 says SATA3 and intel rapid storage says SATA3 as well.
I tried a couple of earlier versions to the same effect, so unless there is some trick i'm not seeing I guess I will just have to ignore it
Run something like Crystal Diskmark and verify your throughput rate. If it shows you are getting SATA III throughput rates, then you will know it's just a bug in Samsung's tool -- and you should report the issue to them...
Oh, and BTW, it is not a "logical" SATA III port; the PCIe M.2 connector has one of the SATA III lanes from the PCH directly routed to it.
1. The benchmark results of your SSD showing that your SSD running at its full performance.
2. By the way, to make me clear. The host physical interface trough M.2 connector is PCI Express 3.0 type - there is four PCI express lines routed trough M.2 connector. There is no additional or separate lines for Serial ATA 3.0 or USB 3.0. The Serial ATA 3.0 or USB 3.0 are using up to two PCI express lines in M.2 connector and are addressed by host trough logical port.
850 EVO M.2 has two keying notches (socket 2 configuration), and is interfaced through the AHCI driver and legacy SATA 3.0 (6 Gbit/s) port exposed through the M.2 connector.