I happen to be putting these valves in now.  I talked to the lady at Andair and got an answer that approximates what you have below.

....However, it would be comforting to have some actual data.   Did you happen to do any testing?

 

e.g. in a 2000 fpm climb you need to lose about 1.5" of mercury per minute to avoid pressurizing.  The worst case would be nearly empty tanks because more volume of air would have to escape to maintain nearly neutral pressure.