Over this weekend, I got a few flights, and it's easy to see the impact of changing the speed and power requirements. I am making flights now with frequent maneuvers as opposed to earlier with more level round and round.
2 flights with APC 12-6 used about 1850 mAh per four minute flight. Pull nicely out hard turns, about 4.9 sec laps.
1 flight with APC 11-5.5, used 1276 mAh, doesn't fly as crisply, lap time 5.6 sec., which feels slow.
1 flight with APC 11-7, used 1736 mAh, performance nearly, but not quite as good as the 12-6, lap times 4.9 sec
Since I have a 2250 mAh battery, the 12-6 is using up 82% of capacity, so 4 minutes with that combo is the limit. A 3500 mAh battery will be needed for 6 minutes (3384 mAh).
As Dennis pointed out, I probably need a smaller, lighter motor for this plane, which should reduce the weight a few ounces and make a more efficient set up. I'm beginning to think that the battery is still going to be too small, but I haven't run the numbers yet.
John