I prefer to use my drysuit for bouyancy in single tanks. Its much warmer. Ocean Water right now is 45f. We are making 2 70 mins dives a day if boat diving or 1 90 min if shore diving. For most dives i am diving doubles so i put air in wing and ds, but if i get cool, i vent the wing and add to Ds. Having air in your suit for bouyancy control and warmth isnt a sin in my books. I use wing at the surface, and if suit fails i have redundancy. Why freeze or bother with the hassle of short dives. Weighting is the same.