Lantirn that's a good reference!
Vilas: regarding the EFATO ECAM. I always thought that the reason for the IMBALANCE line in the ECAM was because of a possible leak due to a rupture of a line or hole in a tank, like a way to cater for an uncontained failure situation.
Like someone said above, "best pump wins".
Most importantly: don't invent procedures, specially those related with fuel.
I had a similar scenario. A 4 hour flight, full house, an imbalance was developing. Fuel checks and leak check confirmed everything OK, except the umbalance, progressively increasing. Captain said do nothing until ECAM comes. It came after a good deal of flight with "cross controls" (slip angle to the left, couple of degrees to the right).
I think it was because of a center pump performing way better than the other, so one inner tank started using its fuel way earlier than the other, to the point of reaching the ECAM trigger point.