Mis-read the OPs original post. Thought OP was comparing a 4 cylinder 4000 to a three cylinder 3000, in which case see my previous comments.
The three cylinder 4000 is considerably heavier than the 4 cylinder 4000, has improved hydraulics, and double reduction axle. That said, PTO HP of the earlier units is about the same as that of the 4 cylinder 4000 (diesels excluded (see previous post))and the 4 cylinder is considerably more nimble.
I've owned and used both and prefer the 4 cylinder for my purposes.
PS is a red herring. Aside from this forum, I've never encountered a "distinction" between "power steering" and "power assist" steering. All power steering is power assist steering, though there are multiple ways of implementing such. Hydrostatic PS is a different animal, however, though unrelated to this discussion.