"The answer to my question about the endurance of the 225 with 19 passengers appears to be about 2:18 endurance (plus 10% and final reserve fuel)."
As per my PM to you, in the 225s I fly you can lift with 4800lbs of fuel plus 19 pax and around 500lbs of baggage, if not more. At a burn rate of 1400lbs per hour this is 3 hours 25 minutes to tanks dry. (BTW, this is how I have always calculated endurance; if I am supposed to take off final reserve fuel and 10% then it is news to me).