A Raw file is bigger, so 1+ second to write one. You could run off a burst of say five of them, and time how long the green access LED stayed on, and divide by the five.
I don't know about the D600, but in D7000, it says the fastest card is a SanDisk Extreme Pro 95MB/s 8GB at 26 MB/second Raw. That is not much more than the Transcend UHS-1 at 22 MB.
In the D800, it says Lexar 1000x card is the fastest (69 MB/second), but that card is not tested in the D7000.
1000x is Read Speed (1000 times the standard original CD drive at 150 KB/sec). Write speed will be slower, and also possibly limited by the camera speed. We really don't know most of these answers.
But the fast card is very nice in a USB 3.0 reader when we download hundreds of images.