All the A330/340 family do that kind of transfer, usually after takeoff - there might be fuel in the stabilizer tank (trim tank) during takeoff, but that depends on the overall quantity taken.
If this particular system is inoP (the aft transfer), there is a fuel penalty according MEL of something like 1.5 - 2% (I forgot, it's been a while now).
So this percentage should be what is saved by having an aft CG.
Nic