I had a 1540 Powershuttle with loader an now own a 1643 Hydro with loader.
I liked the 1540 and its loader, but the one thing about it that completely outclasses the 1643 loader is the floor-mounted joystick. The hydraulics on both machines are a little jumpy (the 1643 being worse), but he floor-mounted joystick allowed you to ease into every movement more smoothly than the fender-mounted stick on the 1643. In short, the fender-mounted joystick is pretty awful.
Now, as far as lifting power, I have always been impressed with the capability of the loader on this 1643. We switched from small square bales to large round ones, and there are many times when we are unloading and/or moving the big bales at 1,600 or 1,700lbs. Obviously, those weights exceed the loader rating for that tractor, but it still does it, albeit at times with a struggle. In reality, I should be using a larger tractor (a 1652 would be perfect), but I bought a 1643 and that's not going to change any time soon, so I have to make do with what I have.
Overall, I am happy with this 1643. It's a good tractor with an impressive loader for its size. The three biggest gripes I have with this machine are:
A. The grease fittings suck. Absolutely suck. Many don't take grease and need to be replaced, but they are a weird thread that nobody carries. I actually had to re-tap a couple holes and replace the fittings with ones I could actually buy locally, but more need to be replaced and it's time consuming and why on earth should I have to do this crap anyway??
B. The fender-mounted loader joystick sucks. The hydraulics are already jumpy and this joystick doesn't help any.
C. Servicing the Hydro transmission isn't easy. I'm not going to explain it all here (I posted a thread about it previously), but if you have one and have attempted to service it yourself, you will know exactly what I mean.
Aside from those three issues, the 1643 Hydro and loader is a good little tractor. Like I said, in hindsight a 1652 would have been the perfect tractor for what we use it for, but I bought a 1643 instead and that's what we're going to continue using for the foreseeable future.