Hawk,
I always use a redundent asystem when Im diving in the Ocean, some times in the quarrys also. Having been trained in teck I am always aware of the need for a redundancy. My pony is a 19 cf, and I also use doubles with redundent systems. My hang tanks are 30 cf., so I have enough gas for a full deco. I hope this helps you, because most of my people use similar set ups.
Clay