Just an update... I bought the Lycom M.2 to PCI-E 4x Adapter and am now getting:
Read: 2602 MB/s
Write: 1535 MB/s
I just wish the M.2 Port on the motherboard was 4x so I didn't have to get an extra adapter.
I got the Samsung 950 pro working (sort of) as my system drive using the same PCIe adapter in a 4x slot,and Magician reports the same as your system - 5Gbps of a max of 10Gbps and running as x2.
My system is a Dell Optiplex 7020 running windows 7 Enterprise 64bit, which only has 1 16x PCIe and 1 4x slot. The 16x is occupied by the video card.
I would like to know if you found out why yours reports getting half of the max shown in Magician. X2 instead of x4.
PS. For anyone interested, I say 'sort of' working because I get a 'no hard drive found' warning during POST that pauses until you press F1 to continue, and then Windows 7 loads fine. I could only get windows to install by disabling UEFI boot mode in the BIOS. Drive is partioned as GPT. Samsung NVMe drivers were needed during the windows 7 install before it would recognize the drive.