I read a review of the D7100 the other day that said the buffer fills in about a second when shooting high fps in raw. If shooting jpeg it goes to 100. If one ever needed a reason to not shoot raw that is it. The same review said noise was more apparent than the competition@ iso400. This was only one review but if it is thought the 400 will soon be announced it may be worth it to wait a while
They might have been using a slow card, I've found that on my D7000 it makes no odds if you're shooting in raw or JPG, the buffer fills just the same and the frame rate drops just when the spec says it will. With a fast card the limiting step is the number of images that can be processed by the camera, if it's a slower card then the write speed could be what limits it.