I don't have the answers to the fundamental questions you ask but a couple of comments. Dinghy sailors have for some years now worn dry suits. These are designed to be worn for quite long periods of time and are pretty comfortable - but not cheap. Even in mid winter, with a few layers underneath, the cold of the water doesn't present a problem for some time, and I guess would give you a far better chance of spending some time in the liferaft assuming you get on board! Some use breathable fabric and even those than don't are not to uncomfortable and are these days easy to get in and out of, leaving your ordinary clothes on underneath with maybe an extra layer. Sailors have also for many years used quick release lanyards for attaching their harness to the boat. These are pretty effective for attaching the liferaft with the ability to release it if the need arises. I guess when avaition meets water their are a few lessons to be learned from sailors.
[This message has been edited by Fuji Abound (edited 07 June 2001).]