If you run one 6s pack, you will likely have some big weight and balance problems. If you can get a way to fit two 3s packs... one on each side, that would be the ideal set up. Balance left and right should be pretty good if not perfect as well.
The larger cell pack will actually benefit performance, as long as the ESC can handle it. Get a fairly low KV motor with the 6s set up, and you should receive a very efficient system.
