Go with the largest gauge, and check out Kimber cables in wall speaker cable. That's what I ended up using and am pleased with the results. It comes in 16 gauge, KWIK 16, and 12 gauge, KWIK 12. Both can be purchased in LONG rolls through Jerry Raskins NeedleDoctor site. Since this will be permanent and hard to change, don't cheap out. You'll regret it in the long run.
Good Listening,
Mike
Good Listening,
Mike