Safety chain strength ratings

I know someone has the answer on the forum, I could not find it.

I was installing my new WDH when I realized my safety cable was too short to reach their latching place on the truck. In doing my research I found that these cables, and all other class 3 safety cables I came across are rated for 5000 lbs. and I could not find any that were more than the 48" ones I have. So I went to Tractor Supply and was going to buy some chain make my own. I discovered that any of the chain they sell only has a rating of 750 lbs. unless you get one of the VERY big links.

Questions: What can possibly be the difference between the chains or cables used to make 5000 lb rated safety chains over what chains Tractor Supply sells?
Where can I find chain rated at this higher value?
Does it really matter?

I am going to Niagara with my old hitch till I figure out an answer or maybe Ed can tell me what to do. Hmmm, maybe take it all with me.