UPDATE:
It's been a few months now, so here are some recent thoughts.
This 1643 doesn't start as easily as my 1540 did. It's not a hard starter, but the 1540 shrugged off very cold temperatures more easily.
For what we do on the farm with this tractor, the Hydro was the way to go, bar none, and we are getting more efficient at operating it. We like how the throttle is linked to the pedals, too. Very good feature.
This 1643 isn't as good on fuel as the 1540 was. Part of that is the engine (4cyl vs. 3cyl turbo), and part of it must be the Hydro transmission.
While the 1540 had a rattle in the ROPS, the 1643 still has this rattle somewhere on the front of the tractor or loader. It only happens around 2,100rpm. Go under or over 2,100 and the rattle goes away.
Headlights are much better on the 1643.
We are picking up and moving large round bales wrapped in plastic and the loader is just...barely...able...to...do...it. But it does it, so we are happy. These things run about 1,100lbs or more, so they're pretty heavy.
Still prefer the joystick on the 1540 vs. the 1643, but we're getting used to it.
That's all for now.