I have a 4420 and have to agree on the beans. nice easy to run combine and easy to work on. I don't know anything about a MF but I have looked at a few and I too are in the situation where I need to upgrade my combine to something close to the same size but with a few less acres run through it.
The 4420 is the better machine in corn, and if properly set, should do just fine in soybeans. Green-stem beans may pose a problem, but nothing works well in those. The 4420 is a better-built machine than the Massey, and should have better parts availability.