Jon, the main benefit (IMO) you get from HMPE and HMPE/LCP blends are: increased stability, increased durability, and reduced vibration (hand shock). You can pick up a little performance increase, but for me the other benefits far outweigh that one--to the point I'd use these materials if they were slower.
9W9, that's one thing that makes it even more frustrating. I have selfbows that I use "high performance" materials on. The only thing different is they have tip overlays--one antler, one horn, one osage. They have held up just fine.
I've also been shooting a Samick Journey for the past 5 years or so--ever since BCY-X came out. I bought the bow just to test the new material. My thought was, if a bow that retails for less than $150 can handle it, it should be good for any. That's all the bow has ever had on it. I draw approximately 31", shooting arrows that are around 8 gpp.
MGF, bows break. I've seen several over the years, had a few break on me. I can only recall one I had that broke with the "FF" string (the rest had dacron), that that failure was obviously not string related. It was a self bow, and it just had a weak spot in the limb near the fadeout.
There's just a lot of misinformation and misunderstanding about strings and string materials these days, sometimes coming from sources you would think would know better.
Chad