#1. "RE: Highest Acceptable ISO for D7100" In response to Reply # 0
If you look at image resources site, he gives a good print size out I the D7100 of iso12800 at 5x7 and the D600 does iso 25600 at 5x7. Also these I believe are from out of camera JPEGs. So with careful RAW processing, should look really good. If you can only get good 5x7's at iso5200 out of a D600, I'm thinking you may need to try some other post processing techniques. Maybe a little less noise reduction to full size images and then down-sampling to correct output sizes for prints....
Look near the bottom of the review for his recommend print sizes vs. iso settings:
------------------ Mark 50 years of amateur photography Currently using Nikon D7100 My walk around lens is a Sigma 18-250mm f3.5-6.3 DC MACRO OS HSM Nikon 40mm f/2.8G AF-S DX Micro Nikkor Tokina AT-X116PRDXN AT-X PRO DX 11-16mm f/2.8 Nikkor 18-55 f/3.5-5.6 AF-S DX VR Sigma 70-300 F4-5.6 APO DG Macro Nikon 55-200mm f/4-5.6G ED IF AF-S DX VR Nikkor Zoom Lens Spiratone 500mm mirror Vivitar DF-383 DEDICATED ETTL LCD Flash Still - and always - learning photography