Air = minutes.
I don't think it has anything to do with not being able to dive an aluminum 80. I think it has more to do with longer dive times. Even with my air consumption, I am getting 80 to 90 minute dives starting over 80 and 90 feet with the deepest around 127.
I know of 2 of 3 operators that use the 120cf tanks, Aldora, Living Underwater, and 1 other. With the extra air, you can dive to the air consumption of the first one to hit 700psi which will always be longer with a larger tank. Depending on the Aldora Boat you are on, that is usually at least 70 minutes for deep dives, usually more. I'm paying to dive, I feel I get more for my dollar with the larger tanks. I also never want to be the guy that forces everyone else to end their dive because I blew through my air.
We just returned from Roatan and there were 30 minute dives due to divers with higher air consumption hitting 700 psi. Bigger tanks mean longer dives. That's what we are there for.
We have dove with people that can make an 80 last a long time, that's great. Some damn near have gills, hell, one lady from Canada had more air when the finished that when she started! (Slight exaggeration) even though my air consumption is higher than some, lower than many, I just don't see how you can have too much air on a dive.....but I can see how you can have too little.
April 16 can't get here fast enough!!
Jay