I think that noise is one of the biggest overblown issues in digital photography.
We expect to see noise free images at ridicules magnifications (100% on screen view = a 5 foot wide image) - that we are viewing from less 2 feet away - on a low resolution (about 100 ppi) display. This gives us an exaggerated impression of the amount of visible noise in an image.
Even when we make extra-large prints, 20x30 (that’s a pretty big print but still half the size of your 100% screen view) and up, we should be increasing the viewing distance. The rule of thumb is that the viewing distance should be the equal to the diagonal measurement of the image – so, a 20x30 inch print should be viewed from about 36 inches back – or put more simply, view the images from a distance at which you can see the entire image all at once.
So, if you can make a good print, without objectionable noise at 8x10 inches, you will be able print that same image at 40x60 inches as long as it is viewed at a reasonable viewing distance, it will look just as good as the smaller print. Remember, that only we photographers press our noses against the glass or study the image at 100% on-screen looking for tiny defects - the rest of the world will evaluate the image when viewed in its entirety.
I would expect that, when un-cropped (or lightly cropped) and properly exposed, the D7100 should produce excellent image quality, at any print size, up through ISO-1600. I wouldn’t expect much drop off in IQ until above ISO-3200 or if an image is cropped by more than half. More worrisome then noise at high ISO is the drop off in dynamic range that makes correct exposure more critical then when shooting at low ISO.
Dave Summers Lowden, Iowa Nikonians Photo Contest Director
Nikonians membership - "My most important photographic investment, after the camera"