I did calculations something like this for my engines BSFC map here:
http://ecomodder.com/forum/showthrea...t-1466-13.html
Also a post at the bottom of page 12.
I was analyzing the effect of Cd reductions and a gearing swap on expected fuel economy during 5th gear cruising. (my commute is all highway).
But your query regarding where to shift gears based upon integrated fuel consumption is very interesting. It would be much more difficult to analyze as you'd need the hard data from the BSFC map. In my case I simply recreated the plotted lines and made assumptions in between....
Maybe theres a matlab script that can take scanned data and convert to real data for a contour plot.