Troy, breaking strength of any line depends a lot of its ammortization ability. PE is not stretchable, so the sharper you pull, the easier it breaks. You can explode 80LB high quality PE buy only 9-10 kg load in case you pull very very sharply. That's why we use shock leaders, twisted leaders, biminitwists and powerfull but flexible rods - all these things take a lot of load from the PE. Though I also noticed that all Japanese PE break at lower loads when they are tested with scales....
Andy, I was a little bit confused about lines with IGFA mark on them, when I knew what this mark meaned. They put this mark on the lines "which breaking strength is guaranteed to be not more than specified on the spool". in other words, in case it is 80Lb IGFA line, it should break at loads less than 80lb. It is very logic from the point of IGFA record rules, but from the point of view of a usual angler like me (not IGFA recorder), I would prefer overtest line instead of IGFA line...
I use both SMP and Avani GT MP for casting, and though I do not have long experience I can not say I noticed big difference in making windknots between these two lines so far. I was of the very good opinion of SMP till your comments of explosion... Fishing is about so many questions and doubts!