My understanding is that an aft CofG means that there will be less aerodynamic download required to be produced by the tail as a trim force.
This download increases the effective weight (because it is a force in a downward direction) and therefore any reduction in this aerodynamic download will improve performance, just as if weight was reduced.
I don't think the drag produced by the trim would be a significant factor during the take-off, although it certainly would be in the cruise.
On the 744, we only use CofG enhanced take-off performance at one critical airport at the moment (MEX) and we have to ensure that we use the chart that is appropriate to the actual CofG pertaining for that take-off. Your post suggested that you are using 25%MAC 'as required', or did I miss something?
There will not be any difference in handling, provided that you are used to an MAC of 25% normally. You are simply identifying and then using the 'extra' 500kg performance benefit that was always there anyway!