The Nikon 80-400 f/4.5-5.6 is exactly the kind of lens that runs into this with a 1.4 teleconverter. At most of the outer end it would be f/5 plus a lost stop with the teleconverter. That puts it at around f/7.1 - so it will AF with the f/8 sensors, and maybe with the middle ground sensors.
The Sigma 150-500 and the Sigma 50-500 are both f/6.3 at the outer end of the zoom. These lenses on the D600 and D7100 are where the problem really comes up. You probably have to use the center AF point on those bodies to have reliable AF - or at least limit your efforts to a few sensors that work beyond f/5.6.