I like mine. I bought it last year to use on a kayak. IQ is strong point. AF is OK,not great. I have not used it with any TCs. Here is one from yesterday. D4s at 330 mm.
Hi Keith, I have the 80-400mm which I use with D4 and I am very happy with . I also have 1.7 tele and have had disappointing results when used with this lens. Having said that I have read elsewhere that the Nikon 1.7 tele is not great generally so maybe 1.4 would be better.
I am pleased with my copy of the 80-400. It works well for me for flight shots as it's light enough for me to hand hold. It does well in good light, but at f5.6 you're losing a full stop over an f4 lens. With a 1.4 tele, it becomes an f8 lens. With the teleconverter it works for static shots but focuses much too slowly for BIF.
I was talked out of buying this lens after ordering the RRs replacement foot.............so if anyone wants the foot I paid $250 for you can make me an offer :)