Okay, so it's not exactly scientific.  But it did convince me that these deck fittings would provide a good anchor for a perimeter line.  The test panel is hidden, but what I did was take a length of 2x4 and bore a large diameter hole in the center to accommodate the loop.   I threaded some nylon rope through the fitting, dropped the rope through the hole in the 2x4, placed the test panel on top of the 2x4 with the loop resting in the hole, and screwed the 2x4 to a support beam in my garage.   The panel is concealed, but believe me, it's there.  Now I could see how the fitting behaved under a load.

I first tested it by suspending  a 21" Lawnboy lawnmower from the rope.   Not that you're likely to need to strap a Lawnboy to the deck of your kayak, but it's nice to know that you have that option.  The fitting took it in stride.

I looked around the garage and couldn't find anything else to suspend, so I went right to the final test... me. The camera doesn't show it very well, but my feet are off the ground. This gave me the assurance that I could haul myself out of the water by perimeter lines attached to these loops without fear of damaging the fitting or the boat.   However, if and when I find myself in that position,  to be on the safe side, I might decide first to detach any Lawnboy that I find strapped to the deck.