Each company should have their own SOP about CTR Tank pumps for takeoff. Ours is if it has 800kg's or less, they will be off to avoid possibility of master caution on T/O, rotation. They are put on during climb or if its really low and one or both pumps won't 'take' the fuel due to body angle then the'll be up on at level off. Don't know about the 5,000kg's or less for the NG, but that's alot! At 1000kg or more, leaving centre pumps on is fine for T/O and climb to CRZ. Imbalance and therefore crossfeed after all this is just a way of life.