Have you tried a factory reset?
lol. Well, I am out of ideas. But from what I have been just researching on the D7100, it does in fact have relatively small frame buffer. I don't know if the size is equal or smaller than my 7000. If it is the same, you are creating larger files than me which would explain the lower buffer. Most people have stated that they were only getting about a 7 shots in the buffer. So I don't think there is a whole lot more that can be done at this point.
If your last image was a heavy MBs i can see it only reading r06,try setting the 1.3 crop see if that changes it.
No, I'm a little nervous about doing that having got the camera set up the way I like it and maybe not getting back to that state. Also, doing it item by item is teaching me a great deal about the camera. We do seem to be getting some progress.