You know as I've thought about this I realized that I have a different situation and different goals perhaps than you Cary are used to dealing with. In regard to your comments about the water getting saturated and after that water movement is more important. I think my situation is different. I installed a 1/2 hp 5cfm aerator because I plan to expand my pond. It has already been expanded 3 times to get where it's at. My pond has two larger oval sections connected by a narrow channel. So I put a diffuser in each main section hooked up to the same pump. Since I don't need all the air that this system puts out my goal is to run the system for the least time possible to save cost. In this scenario my need is to keep the DO up high enough while avoiding running 24/7 and therefore I do not have the situation you describe where diffuser efficiency doesn't matter. The more efficient air stones should allow me to run less. My pond might be cleaner if I ran all the time since max DO and max movement tend to allow everthing to work better. But, when my system is on it's large output really moves things around. This is my situation and hence my contention that air stones are better for me than rubber diffusers. I run my system for two 4 hour periods each day. I don't have equipment to measure DO but I've never had a DO problem that shows itself. This is all seat of the pants and I'm afraid I'm way behind many of you in the pondmeister science.
