For what its worth, if you have a 240V - 50A, set it to charge at 12 A if can (time permitting of course). Losses are i^2*R. Therefore if you charge at a lower current for longer, you do so more efficiently.
I think peak charging efficiency will require a bit more power. A good chunk of that juice goes into the cooling system instead of the battery; that's why 110V charging is so slow. It has been reported elsewhere on this forum that 240V 30A is the sweet spot. 40A is almost the same.