There are quite a few questions in your post; and you're an experienced tractor owner. All I can write about is my own experiences.
The only tractor I've ever owned/operated/maintained is my 4105. I'd never owned one before (and hadn't discovered TBN to ask questions of this august group
), so I questioned my neighbours about who had the best reputation as a dealership & my tractor needs. For my area (State, actually. But Tassie is small) JD came out as the most recommended, so I took a friend (old YANMAR tractor owner) to the JD dealership and sat down with the salesman (a farmer himself).
The bloke listened to me, asked pertinent questions about what I needed the tractor to perform, eliminated whole 'classes'/series and then recommended the 4105 as it was actually less expensive (bare bones) than others that he could have sold me. He sold me a tractor that I needed at the hp that I needed.
My
local JD dealership has stood by their product, and me, ever since.
ath: Mind you, in Tassie (an island State) reputation is KING and word travels fast if a business is less than 'supportive'.
I have had zero problems with my JD tractor and it has done everything that I've asked of it within its capabilities. Parts and support are readily available from my dealership.
Now, the 4105 (41hp) model is no longer produced so I can't recommend a current model.