Your financial calculations appear to have overlooked one very important regulatory issue. Don't forget the max legal flying hours per annum is 900 for Cabin Crew & pilots. The round trip to New York in a 767 will be near enough to 15 hours; thus the maximum number of trips per year will be 900/15 = 60. Or 5 trips on average per month.
Removing leave (4 weeks per year is UK legal minimum, for details see
http://www.opsi.gov.uk/si/si2004/20040756.htm) your max would average 5.5 trips per working month). In any case 60 trips per annum will be your absolute legal maximum and may be difficuly to achieve.
If the average trip duration is 50 hours (bet it is less) then the maximum flying allowances per year will be 60 x 50 x £2.30 = £6900 or only £575 per month!!
Thus the absolute maximum monthly salary before tax could be only: £875 + £575 = £1450