For me, the most emotionally powerful is the sonata in E minor op.90.
Really? I played that work, and while it is very powerful, it still doesn't measure up to the last three.
I have some bootlegs of Hamelin which are, believe it or not, really good. Charles Rosen also has some good recordings of the late ones. There are many others I like but that don't come to mind.
Yes, I have, and I didn't care for them at all. As a matter of fact, I don't think I have ever cared for any of Feltsman's recordings. You aren't the first one to recommend them to me, either.
I have a soft spot for op.78 in F-sharp major.