It depends on what type of photography you do. If you shoot mostly landscape, street, use flash, or shoot jpegs, then there's not much difference. On the other hand, if you are a wildlife or sports photographer, they fixed THE biggest complaint against the 7100, buffer capacity. If the ISO performance is in fact improved by two stops, well that's pretty awesome and would put it on par or better with the D810. Third, improved AF is always a good thing.
So depending on your needs it is either a major improvement, or very little. If none of those improvements are important to you then you likely saved some money buying the 7100.
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