Been running 40' MacDons with the factory HUR plus a 3' extension and it can still be tight to get to the middle of a large grain cart. That puts the auger to 25.5' long, the new 2010s have an optional 26'. It only costs a 1000 bucks from stewart steel to get the 3' extension, I don't know how close you are to Manitoba but I could direct you to a dealership that has 4 used ones. They were ours but we traded them in on the new 26' auger and were no longer required.
Its power to weight ratio combined with the added weight and volume potential of the larger head. The 9660 won't be able to push it to its full potential like a 9860 might.
Well Muddy your probably the first one to say that a 9860 is a 96 with a big motor and the only difference is the decals. I'm not sure what you mean about power to weight. The weight of the 96 would be very close to that of 98. Maybe you mean header width to capacity?
As far as a 40ft on a 96 it would be great for crops like peas, lentils, soybeans and even low yielding wheat.
which is mostly what we will be using it for. we thot it would be better to drive slower than try to load the machine with a faster ground speed, since some of our cutting conditions are not the smoothest. it will be used for soybeans, peas, other types of edible beans, and wheat, which we dont usually run into wheat above 60 bushel.
I agree that the 9660 could handle it too. As long as you have a few main items like heavy duty reverser, hi cap lift cylinders, and decent front rubber it would work just fine. Throw a power chip on if it seems a little doggy.