At what height are you flying?
The range for the A-8 with 640ltr and no drop tank was 615km (0.3km, 1.20ata) to 1035km (7km, 1.05ata) depending on the height flown.
Are you including warm up, taxi out, take off power, climb?
For the A-8 Fw, had a 12.5% reserve.