The only bad thing about a 8570 is the ladder going up to the engine compartment,its ok if your hands are free but if you have something to take up there its a bugger,other than that they are a bullet proof combine.
The 8570 is a great machine. The biggest advantages of moving up to the 8780 are the cab, increased hp, 240 to 260 (285 in XP),and the constant speed rotor drive. The constant speed rotor drive keeps the rotor speed the same even when the engine pulls down. This can NOT be added to an 8570. I am not putting down 8570's, just want to make you aware of differences.
Owned an 8570 for 3 years, I was very impressed with capacity and serviceability. No major breakdowns in the years I ran it. As stated only change to 8780 is HP boost and cab refinement. Just traded for 8780XP and am wondering how much improvement I will see. Be sure air cleaner has extension to raise it, I had to change air filters every 150 hours without the extension.