According to the boing flight trainning manual if your objective is to save the maximum amount of fuel for the entier flight (extra long distance to cover) the full thrust T/O and full climb is a better choice. Provinding you are not leveling off until you reach your final cruising altitude. I belive it's because you'll be reaching the said cruising level faster so you'll be burning less fuel. Although I agree with BOING on the long time affect on the engines. The savings from a full thrust would be only profitable for a tight flight fuel wise.