I did some destructive testing with my idea of the adjustable diamond knot attachment. Basically what I came up with is that the multiple diamond knots are stronger than the line with spliced loops at the end that I pulled on it with.
I did a very simple eye on both ends, one of them whipped so as to make it an adjustable eye to put over the diamond knot, and a non-secured eye on the other end which I either put over a bolt in my steel table, or luggage tagged to an endless loop that I then attached to the table in some way or another, for adjustability. None of the splices slipped.
I then put the adjustable loop over the outermost of 5 diamond knots at the end of a loop, then luggage tagged the multiple diamond knot loop to a shackle and pulled it with a come-along with a deer scale on it so as to be able to observe the tension at which it broke.
I used 1.75mm dyneema of some sort I had lying around; it is probably be Samson Lash-it, which has a stated breaking strength of 400Lbs.
In 8 tests, in only the first one did a diamond knot fail. It slipped at 350Lbs and failed at 375. It was the first 5 diamond knots I had ever tied in my life. I imagine that the legs were of uneven lengths, as I had trouble making the knots come together evenly.
In all of the other tests, I was not able to break any of the diamond knots on the second set of 5 diamond knots I had ever tied in my life. I am sure were better, more consistent, and tighter than the first 5.
The line mostly broke at the end of the taper in the splice a about 300-400Lbs, even though I tried to make nice long tapers, and I broke one eye at the end where it was hooked onto the diamond knot.
All in all, I am pretty sure that the multiple diamond knots in a row are all at least more than 100% of the strength of the line with loops, which was what I was hoping to prove.
I am assuming that the results would have been the same with the larger line I plan to use, but may do a test later to make sure.
Here is a link to some of pictures of my test rig, and the carnage
https://www.flickr.com/photos/959099...7651093139326/.