Be very careful!
"your FMS will probably tell you what your landing fuel will be based on the new airspeed and power settings or you can easily enough calculate it"
This is exactly the cause of the Airbus 300 which ran out of fuel at Vienna in 2000
Hapag-Lloyd Flight 3378 - Wikipedia, the free encyclopedia
The FMS will possibly not have the capability to use the actual fuel burn figures, it may use programmed data which will not be accurate!
Happy landings
3 Point