Posted for "Carl LaRue" <c.larue@verizon.net>:

Bill, I carry O2 but generally fly where I don't have to use it.  I haven't
plotted my 4 PSI curve but memory from recent trips tells me that cabin
altitude is 8500 feet at FL 190 and hits 10,000 feet between FL 22-230.
Trip length and wind component dictate what altitude I fly at, and it seldom
has to be  above FL210 for efficiency.  Now that you asked, I'll start
plotting it for myself.

Carl La Rue