Turkeyboy, could you tell exactly where the break occurred? I'm guessing at the pinch in the rings, but I would much appreciate learning all I could from your experience. I'm experimenting with something similar, though with 7/64" Amsteel Blue. I think I'll hang a little lower...
On page 40 of the Samson Rope Catalog is the following note:
"Where a rope bends more than ten degrees around bitts or chocks or is bending across any surface, the diameter of that surface should not be less than three times the diameter of the rope. Stated another way, the diameter of the surface should be at least three times the rope diameter. A four-to-one ratio (or larger) would be better yet because the durability of the rope increases substantially as the diameter of the surface over which it is worked increases."In your first picture, it looks to my untrained eye like the turn radius might be a bit tight, especially the last turn of the Garda hitch at the pinch point. Not saying that's the case, though, and it's certainly no different from what I'm doing with 7/64" Amsteel Blue and SMC descender rings.
I'm speculating, but the tight radius might have transferred much of the tension load onto the inner radius of the protective outer braid, off of the Dyneema core where the strength is. Perhaps single braid line might fare somewhat better. My derriere sure hopes so!!
(2nd edit: Got my physics bass ackwards... the outer radius should have taken up the load... sorry 'bout that!)
Maybe someone with the relevant expertise can offer some insight on this.