An aft C of G is highly preferable for the cruise as it minimises the moment arm between the centre of pressure and the C of G, thus the force required from the tail is reduced. This allows the a/c to fly at a lower AOA as less lift is required and so the induced drag is reduced.
This should also apply in the climb as this tends to be at a lower speed, where the major component of the drag curve is due to induced drag. An aft C of G will again allow a lower AOA for the same lift and thus the max residual lift will be higher.
Obviously you also have the issue of stability being adversely affected by an aft C of G. Some A/C (most of the Airbus birds as far as I know) run an aft C of G which is very close to the centre of pressure. They require several computer systems controlling pitch to make the aircraft controllable!