That sounds perfectly normal to me.
nMP gives PCIe 2.0 x4 lane to the SSD slot. So, the bandwidth is 2000MB/s.
With 20% overhead, that real world max should be ~1600MB/s.
And 12xx / 14xx MB/s seems very normal for a x4 5GT/s connection.
I was actually replying to avatar1349; didn't quote because there wasn't a reply between the two posts when I was replying.