G70 5/16" is plenty. Get good ratchet binders, trust me they are worth the few bucks extra. Lowe's is the cheapest place I have bought it but I am sure it is Chinese chain, it has held up though. I would think weight and shipping would make online ordering cost prohibitive especially on the chain. You are gonna spend $200 or so to get a set ( 2 each) but they will last a lifetime and when that jackass runs you off the road and your tractor is still on the trailer it will be worth every dime. It happens more than you think.