ony hypothisizing here, but I would think that they would be capable of some quite high loads, the effect of choking own on the biner attachment would distribute the force quite well don't you think?
and while yes all that's holding the end beyond the (dare I say) splice) together is the whipping, a good whipped only eye can be pretty strong providing it is around a object which the load can be disributed to, I am also thinking of the running bowline principle when pulling over a spar, (with appropriate mechanical advantage, a 5:1, not a 8 cylinder)
and how little force seams to be applied to the bowline itself...
Of course I am in no way promoting or suggesting that it is safe(CYA) but I wonder when, where it would break? hook it to the 5:1, anchor , apply a force, get the truck whatever, test it out, tells us what you find...
Herein lies some fun to be had this winter, testing things, fun fun