Everybody says the 9770 will do the same as the 9860 will but both our 9770's we've ran this year will not hold a candle to our 9860. They do fine till the unloading auger is on in higher yielding corn (200+) then it seems like the horsepower is cut way back and the 9860 doesn't slow down any. The only thing we've ran them side by side in is corn so I hope this helps.
We have been runing a 9770 with our9860 premiums(which have a little mor hp) in wheat barly and canola. In wheat it was running a 30 foot draper against 36 on the 98's. It could keep up. We had some wheat and barley swathed at 36 feet and it just couldn't keep up. That last little grunt seemed to be missing. About .6 mph slower. Had a 8120 out for a day and wasn't very impressed. It kept up but that's about it. I will admit though we haven't run caseand it was only one day