Max speed of M.2 drive connected to PCIe Gen2 x2

Mar 28, 2018
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Hi everyone,
I was planning on getting an M.2 drive for my pre-built small form factor PC (ASUS ROG GR8 II).
The website indicates that the M.2 slot supports up to PCIe Gen2 x2 bandwith.
High performance drives, such as Samsung's 960 Evo, will obviously not use their full speed, since the require a Gen3 x4 connection for that.
Does anyone know what's the max read and write speed I can get out of this slot?