Hi dkipta,
I have the same mixer. I have gone as high as 1000grams(7-8cups) of High Gluten flour with 60% hydration, It makes 3 1/2 pounds of dough. I am not sure if it can handle more than that even though Kitchen Aid claims otherwise. You may be able to use more than 7 cups of flour using a lower protien flour like all purpose? The biggest problem with these Kitchen Aids is that the dough tends to stick to the hook and spin in circles. In any case they are durable and will be a improvement from you're smaller bread machine.
Chiguy