The 3 cylinder general purpose ford tractors are the next generation of what the hundred series is and they are vastly improved with the same "bullet proof" kind of reputation. I still have an 850 and a 640, had a 3600 too, and since '15 have had a 4630 FWD/. 4630 with the features mine has, is just miles ahead of the 850. Between the diesel 3600 and the 850, it too is just more tractor, differential lock, power steering, optional 2 stage clutch, 3 cylinder diesel being easy on fuel, no comparison. However both are very good, will do a lot of work and purely capable of most general purpose tasks, just the newer 3 cylinder models are better with more modern features. Maybe not a good analogy, but the hundred series is to the M1 Garand Rifle as the 3 cylinder models would be to the M14 or M1A rifle. Both very good tractors, just the newer ones are just more modern and I think the best bang for the buck. Power steering on my 4630 is just about 1 finger operational, it is a pleasure to drive, but so was our '64 4000 with S-O-S transmission, it too was easy to drive.
The 4630 I have is perfect for every task I need it for and it does not even have a loader, never did, was a good buy and low hours. Hard to go wrong with a 3 cylinder general purpose tractor that is in field ready condition.