Great info! I bought a 9AH battery last year, and found that it has many advantages:
1. Being new, it's performance was what was specified. My older batteries seemed to be providing less current, and also less capacity
2. It has a lower "C factor", since it has a higher current capacity than smaller cells. Even though the smaller batteries worked OK when new, and when it was not too cold, they had less margin, Age, cold, and less than full charge caused them to stop spinning my auger reliably. Zero problems will the larger cell.
3. I could go out with less than a full charge. I drill all day, and go from 3 bars to 1 bar, worst case. I stopped charging at 3 bars (out of 4), and always had more than enough capacity. Per the graphs, I should have near full performance as long as I am fishing.
I am betting that many problems people have with drill driven augers are caused by small, old batteries. They have to work so hard to produce full torque on a drill driving an auger, that they are degraded quickly.