Some snippets
Similar to Rainboe, I've also had the cabin depressurise in the cruise - because of a faulty gear squat switch. The aircraft was suddenly convinced it was on the ground, and one of the results was the cabin dumped all the pressure.
Flyinwithoutwings: You might want to look closer at your emergency descent next time you are in the sim; you quote 2500 fpm - for us, that would be a slightly expidited normal descent, whereas an emergency descent is well in excess of 4000 fpm.
The available oxygen increases quickly as you descend, and depending on the oxygen equipment, rate of consumption of the supplemental oxygen reduces as well. Once you pass 22,000 descending, you can take your time getting to 10,000 because the amount of suplementary oxygen you need at, say 14,000, is practically speaking negligible. (This is not to say that you or your passengers can be oblivious to a pressure altitude of 14,000 feet - they will get a headache, have difficulty sleeping, feel hot, and struggle to complete the crossword. Your passengers will however not die at 14,000 feet, even if you stay there for an hour).