Allen,
Physically, the cub was built to be a 2/3 model of the A. I'm guessing, but that should mean that the A is just as stable as the Cub, or maybe it is the other way around since the A came first. The A is capable of pulling a 2-bottom plow, which is a bit of a push for a 20hp engine, so many of them have been setup with extra weight on the lighter wheel, to prevent wheel spin. It is easier to manage than having to ride the right brake all of the time. Which is another thing that you often run into on As, the right brake is shot from being ridden all of the time.
The A is a real workhorse. I loved the one that I had, but it had been rolled over at some point in it's life, and when someone made me an offer on it, I had to let it go. I will definitely get another at some point in time. You made the right move, getting the A for the loader. The loader is a bit too much equipment for the Cub, but it was specifically designed for the A, and will not bog it down like it would a cub.