Well, after reading through this whole damn thing, I have a couple comments, and I've been out of college so many years that none of them involve calculus. Regarding the post where a 180# object will slow down faster (if thrown up) than a 2# object...if they are equally dense, they will slow down at the same rate. The reason this is an easy mistake to make is that a person can THROW a 2# object pretty fast...so, of course, it will go higher than a 180# object, which can't be thrown very fast at all. IF you could throw them at the same initial speed, they would go the same distance up (again, if their density & aerodymics are similar.) Like the example about the falling feather & a falling lead weight...in a vacuum, they fall at the same speed. In air (or water) their different densities....not weight!....cause them to fall/descend at different speeds.
The other comment has to do with whales breaching. Whales, of course, attain a certain velocity when they breach...but they can continue to propel themselves with their flukes even AFTER all of their body (except the flukes, of course) has risen above the water. Kind of like water polo players who can keep about half of their body out of the water even though they have no vertical "velocity"...just kicking & sculling against the water to keep high in the water.
Back to the original question, I don't think a human could ever breach the water as described....and I'd think a good freediver, kicking hard even as they broke the water's surface, would get higher out of the water than something (a runaway ascent diver) relying on buoyancy alone.
(actually, I've joked with divers when we have rough conditions....I tell them that instead of climbing up the dangerous ladder, I'm going to fully inflate them from about 40m/130', and have them jump right onto the boat, like big neoprene-clad penguins.)
