In early 1977 my Dad and his partner were looking at buying two new tractors for our farming operation of about 3000 acres of row crops in Alabama. They were looking at the IH 1086 and the JD 4430.
The IH dealer had a couple of left-over '76 model 966 Turbo's and he said he could turn up the fuel pressure and make it pull like a 1066 or 1086. He offered them a really good deal for the pair, and they took it. They came with cabs and A/C, our first tractors with A/C. I thought I had died and gone to heaven.
Anyway, those two tractors proved to be truly excellent and have paid for themselves over and over and over again. They are still in the field and everything still works on them. We've taken good care of them and have never had a catastrophic failure in either one of them; they have never let us down.
The 966's and 1066's have enough weight to put all that horsepower into the ground. The only weak point that I've ever seen in them is the hydraulic pumps. We've not gotten the life out of them that we have with our JD tractors.
We have a somewhat newer vintage JD 4440 which will out-pull them, and is a little more comfortable, but the JD hasn't held up as well and has required more repairs and is a little harder and more expensive to work on.
These 966's use more fuel than newer tractors, but are comparable to other tractors of that size and vintage, and they just keep going and going. My dad and his partner considered those 966's one of the best investments they ever made.