Mutt -
BE400s come with a variety of O2 bottle sizes..some are little, just big enough to get down from Alt to 12500, others are for extended flying..
I think some reality should be put in this thread..
If you do this trip, your getting updates on Bermuda's airport...the chances that it is destroyed while in the pattern is pretty remote...so you have 587 miles to turn around...
Even if over Bermuda, the airport goes down, you can stay at alt, fly home easy...if by chance you lose pres as well...you could go EMER to say FL240, then say 100% till the bottle runs out, depending on size...and if it does en route...then drop down to 12500 to 14000 for the rest of the trip.
I calculate flying over at FL390 then flying back at 12500...no problem...the O2 bottle wasn't in the equation with regard to fuel calcs..so assuming a small bottle, you just use it get down fast to 12500...fly home...
No doubt if you did this trip allot you'd set up the plane with the big bottle to be safe.