Hi,
This is a bunch a tricky marketing mumbo jumbo.
If you are seeing 800 MBps, you are getting 6.4Gbps... not bad. Keep in mind 10Gbps is maximum theoretical, not actual throughput you might achieve.
Your m.2 drive is PCIe 3.0 spec capable of x4 but the number of PCIe lanes available on the Z97 platform might be affected by CPU and the number of devices connected to your board which could, in theory limit the number of lanes available to storage. Further, the way a manufacturer implements support can affect the actual speeds you achieve.
Choosing Samsung is the best you can hope for as far as storage goes.
Now see the boards chipset implementation. There's a "switch" between the Z97 and m.2 interface. What is it? Maybe an enhancement that allows PCIe (2.0 spec) to operate at x4.. I don't know. But you can see how things get implemented differently between manufacturers.
Maybe someone else who has more expertise here will jump in.
