I have the 930 and the 915 models. The bigger one is my main summer canner, and when doing big projects, I often have them both going. (Boy, is our move going to change everything! There is a glass top stove in the apartment... I don't have any place to put my 40" professional dual fuel stove. Sigh...)
The 915 (holds 7 quarts) is perfect for canning small batches of "planned overs" (leftovers created by deliberately making way more food than we can eat at a meal). It great for canning, say, 5 jars of soup while cleaning up the kitchen... because it's smaller, it gets up to pressure faster and cools down more quickly, too.
I thought about getting one of the huge 940 models, but decided the 2 I have are the best solution.
Summerthyme