Might I suggest that the load bearing ability of something like a quick link, and its ability to take a great deal of shock, may be two very different things. If it were me, I'd get quick links that could carry much more weight than I believe they would be forced to carry just to be safe, as long as their size allowed me to use them of course.
For example, I have a 6K pound trailer. I would try to get two 6K pound quick links, as long as their size would allow me to use them on my safety chains and attachment holes on my hitch.
ETA: It appears there are 7,500 pound 1/2 inch quick links avialable from eTtrailer.com, so they are out there.
The odds are in my favor that I will never need them, but if I ever do, ...
I'm am *not* a big fan of surprises.