When I first got the 400 in question, I also got a TC-14 (no letter suffix) teleconverter, which is, I think, the AI verion of what became the TC-14B for AIS. I found it worked pretty nicely with the 400 on film, and the quality seemed quite good. I haven't done a lot of comparison recently, but back when I first started shooting digital with a D3200, I tried it just to compare teleconverter use with cropping. It seemed about a dead heat, and not too long after that I got the 200-500 anyway, so the TC-14 hasn't seen much use.
I'll have to try it again in daylight, with the D7100, and see if I can do a better test.