John, get off the "single tank stuff"! No one should advocate doing any dive with any amount of air/gas that won't be enough. As I said on another thread, I take 50% more gas that I plan to need.
I think there is actually a place for single tank discussions, with competent buddy teams like described by Thal, and larger than 80 cft tanks. There are probably a few female instructors in my pond that have hit 160'-180', as a team, with single 63 cft's, and returned quickly to shallower than 80' where the remainder of the multi-level dive was over 30 minutes.
If one looks closely at my OP, I did not indicate this discussion "should be" about single tank. In order to help those most in need of help, it is possible that subject should also be discussed.