A certain wide-bodied turbofan is expected to perform as follows at M0.8 ISA over 2000nam with FL350 and FL390 available. Apologies for my slight rounding of figures to protect the innocent.
GW kg; Payload kg; Block Fuel kg; Reserve Fuel kg
137000; 20500; 19700; 5450
141500; 24300; 20300; 5600
(146100; 28200; 20900; 5725)
(150600; 32000; 21400; 5850)
Increasing the Gross Weight by 4500kg from 137000kg increases the burnout by 600kg, adds 150kg to your reserves giving a nett gain to your payload of about 3800kg.
So, crudely speaking if you tried to tanker 4500kg for 2000nam you’d burn off maybe 700kg in doing so. Sorry it is a bit rushed.
I used p55 of
Boeing: Commercial Airplanes - Commercial Aviation Services - Flight Operations Support - Airport Technology - 767 Airplane Characteristics for Airport Planning to rough out my figures but downsized contingency to 5%. Also, and don't quote me, at 154300kg M0.8 the CL of said 767 is 0.5 at FL350, tsfc is ~ 0.59 and the sar is ~ 93nm/1000kg.
Best Rgds
The "E"