If the wires on your packs are 12awg I would be worried. If they are 10awg then you might be right. It all depends on how much you are going to load your motor up. If your setup draws a fair bit less current than what the MMMXL is specified to handle then you should be OK. If you are going to push it to it's limit or even close I would go for 8awg wires all round. If Castle can see merit in using 8awg wires on this ESC then I would say that the batts should have the same.