You've got two advantages working for you with the welding cable, bigger conductors, and more strands of wire. Since current is carried mostly on the surface of a wire, the more strands there are, the better. I think 2-0 is a little overkill, however. I've used #1 or #0 welding lead with good results, even when there's a long cable length. Be sure the connectors are soldered, not crimped, if possible. The standard 6-volt cable is a #2, or sometimes a #1 wire, but the strands are a lot coarser than welding leads.
Jerry
