I'm not willing to put much into this one because I don't know that there's anything to prove one way or the other. 

To be honest I haven't got my head programmed to think about the late model machines where the engines have their tails all twisted up in a not.  Might be different with them then with the 200 hp 466's I was thinking of....the ones you find in worn out combines.   

Combine application is a lot like a stationary power application....start it up, warm it up, take it to rated speed, and run it steadily for a long time.

Tractor has varible spped and varible load constantly.

Probably doesn't make much difference.

Combine engines usually outlast the machine if they do not die from some sort of neglect.

Deere's most common cause of failure for many years was the stupid drain hose on the oil filter housing.