You're not going to find too many fans of the Champion on this forum. There are better toilets for less money. Like the totos.
However, it is my educated wild-ass guess that the Champion Max should be somewhat similar to the Champion 4 in performance, as they are just turning it into a Watersense (1.28) toilet, and probably copying those who went before (like Toto) as to how to accomplish that. It's the quality control at AS that we all still cringe about, based on the anecdotes that are posted here and elsewhere.
The Toto Promenade CST424SF (1.6gpf) if you can find it, or the Toto Eco-Promenade CST424EF (1.28 gpf) are both excellent performing toilets at chair height and round bowl.
Are you sure you need a round bowl? There are elongated toilets that are comparable in actual length to round ones if you do the research. Also, we find that unless you have a physical object that is going to hit the bowl (like a door), then elongated is the way to go even if it appears at first blush that it will take up too much room. I made that mistake with my round Drake; an elongated would have been fine. I would look at the Original Drake CST744EL or CST744SL as options. They are excellent values, but both are elongated. The Drake II has chair height, CEFIONTECT finish, a flush with a little better bowl rinse (double-cyclone), etc., for just a little more. CST454CEFG
When you are pricing Totos, never go by list price. Those are the prices your decorator would charge you if you had one; the real street prices are substantially-less, and you can get an idea of them by doing research and by calling multiple plumbing supply stores in your area with an exact model number and color in hand. You will get a crazy range of prices, some of which will be close to what you see it for on the Net and some of which are similar to the list. But with a little effort, you can find a fair price.
Good luck!!