I'll also note that the big differences in HMPE materials are stretch, creep, durability, and noise. Sometimes these differences aren't so big, and all of them can be affected by how well (or not so well) the string is made.
100% HMPE or UHMWPE materials may show a slight benefit in performance, because Vectran is heavier. However, in a material like BCY-X the percentage of Vectran is so low (17%) that the difference is hardly noticeable even on wheel bows, much less ours.
Materials with Vectran seem to be a little quieter--or maybe it's just a lower pitch. I don't have the instrument to measure noise, so I'm going by the human ear--mine and many others.
Vectran will make a material more stable, especially when the temperatures go up. Even the highest grade of Dyneema (SK90) can be affected by heat. The lower the strand count, the heavier the draw weight, and/or the longer the string the more it will stretch/creep in higher temps. Not a lot and nowhere near the amount you will get from Dacron/polyester, but more than you will get from the HMPE/Vectran blends.
In the end, shoot what you like. If you can, try out different materials and strand counts and see what works best for you. Don't base your decisions on smoke and mirrors and secret formulas. Ask lots of questions. Don't be afraid to go to the source. I know BCY is great about answering questions about their materials.
Chad