With my scuba I get 1-2 fills real high, 2800+, from then on it's down hill. It lasts a very long time...you'll have no problem going a day with a scuba...two is pushing it if you shoot a lot.
When I play we have about 2 scubas and about 5-8 tanks. So air goes by quite quickly, and we have to have the scubas refilled for the next time...but we have no problem getting through the day.
Carbon fiber will always be lighter then steel tanks.