At first when I got the D7100 I set it up similar to my D800. But since I really only shoot RAW, I assumed that the 6FPS spec was good. However the R-number in the lower right of the viewfinder said 3. And sure enough the buffer filled up after 3 frames (about 1/2 of a second) and then proceeded at 1 frame per second continuous. I tried high and various low settings but the buffer seemed to always run out. So I got tired of this. I went through all the shooting parameters by turning everything off and then turning them on one at a time. Here is what I found for Raw only, 14 bit, lost less compressed:
Auto Distortion Control went from 6 off to 4 on,
Long Exposure NR went from 6 off to 5 on,
Auto ISO sensitivity went from 6 off to 5 on.
And sure enough if you turned all three of these on, the rate went from 6 to 2. Wow!
Now, of course, for you JPG shooters the numbers will be much higher but one thing I did run across was that you numbers will be higher if you choose size-optimized rather than quality optimized.
If anyone else can add to this "small buffer for raw" problem, please contribute to what we can do on our end (the Nikon customer). Oh, and yes I do use the San Disk Extreme Pro (95mb/s and UH/1) and I've tried it with and without grip and one card and two. I didn't try raw + jpg - it is bad enough just Raw.
Question for the technically minded: Any chance Nikon can improve the Raw speed in a new firmware release? Canon did it with the 7D a year or two after release.