. And third, in such a situation, 500 lbs is more then enough. You don't have to get all the way to the surface on it, just close enough. If I were at 100ft and had no air, trust me, my weights would be off and I would get back to the surface. I would much rather spend time in a chamber then a coffin. The closer you get to the surface on that 500 lbs of air before ditching your weights may just make a little difference.
Are you saying that 500 PSI is enough to get the two of you to a depth where you can both do a CESA or a buoyant emergency ascent to the surface? I personally think that I can do a CESA from 100 feet safely, but that's not how I plan my dives.