ouch guys, lol.
If you control your breathing volume you could get through a dive if you were real close to your perfect weighting. I also did say add a few pounds to the neutral full tank weighting when using aluminum 80 tanks. You all seemed to confirm that. It is of course easier to control being a little over weighted than under. You just use more air making adjustments with your BC all the time.
But if you are only a little under weight safety stops can be done i.e. through the use of breathing control. Many instructors do it when they have handed off too much weight to their students. The emphasis is on little under weighted. It is not the best course of action but is possible. This of course would be easier for those of us who have larger lung volumes (rib cages) to play with. Spectrum you are right in that it is something that should not be recommended to new divers. Thank you for calling me on it. I only meant to say it could be done. I did not mean to recommend it, and in rereading what I wrote I could see that interpretation.
But ultimately my intent was to recommend weighting with a near empty tank. I am sorry if it did not come across that way in type. That is the best method I know of short of doing the physics equations. By the way good job on that Mark looks like you have that end covered! I did not check all the numbers but on first read it looked accurate. Try to get that info printed on dive slates, and you might have something marketable.
Further if you are a new diver following a sloping bottom or descent lines and being slightly over weighted would be safest.
As for the BC ideally it is supposed to be used to offset changes in buoyancy due to compression of your thermal protection, provide lift for things like helping another diver to the surface, and/or provide positive buoyancy at the surface for resting, etc. That is why you have to exhale at the beggining of your descent because you are supposed to be close to nuetral. If you were grossly over weighted you would sink with a full breath of air reguardless. I do not think mobsters with cement shoes exhale on their way down to meet the fishes. But it sounds a little like maybe you guys are wanting to do a science experiment along those lines on me right now, lol.
The best method is with a near empty tank like I said in the first post, and you all seemed to confirm that.
I am glad to see others take this sport as seriously as do I. Finally, by all means question anything you hear from any source. Ultimately, your safety is in your hands dive prudent and conservatively.