specimen figures
Good answers. I back engineered the data a little bit to try figure out the F390 part.
Let us suppose B737-800 OEM 41413kg, ISA+10, 69600kg take-off with 13500kg payload for 2000nm block distance is just eligible for F380 at M0.78 with a climb burn of 1500kg. Thus at ToD we are at 68100kg say. Instantaneous climb performance reserve at constant 247kcas is 630 feet per minute, L/D 17.4 for a lift coefft of 0.61, tsfc 0.65kg/kg-hr and a buffet margin of 1.39g. Breguet Range Factor is (V/c) * (L/D) so roughly the RF is 12050 to slide rule accuracy. Provided that this does not infringe any limitations, fine. But if it does and/or a better RF can be found at F360 this is what the FMC will suggest for optimum.
At the higher lift coeffts the aircraft tends to run out of buffet margin and climb performance. If L/D falls off too much the engines have to work harder and the tsfc starts to enter hot country.
Given that the computer chip is probably still a common or garden 386 I’d guess the sums are largely based on lookup tables.
Factor in what the other guys are saying, especially the coffin corner warning. But essentially don't poke the bear and don't thrash the engines. You can get away with the latter but if you attempt the former you may run out of sky.
I hope that helps.