D-10 is 100% Dyneema. Think Dynaflight '97. The highest grade 100% Dyneema material on the market is BCY's 8190 Universal, made with 100% DSM SK-90 Dyneema.
BCY-X is 83% SK-90 Dyneema blended with 17% Vectran. Think 452X. The Vectran stabilizes the material, especially in higher temps, and seems to act as a dampener as well (quieter).
I don't think more strands gives you better performance per se'. I just haven't been able to squeak out a noticeable difference between a moderate strand count and a low strand count. What I do notice is less stretch, less creep, higher durability, and higher over-all stability. Olympic and Olympic style shooters usually go with what I consider an over-built string (high strand count) for the best stability.
Will the average 3-D shooter/hunter notice the difference in stability at the distances we shoot? Probably not, anymore than we will notice 1-3 fps. If either one is a game changer, you should be shooting for money and Olympic medals. Seriously.
It boils down to what you like. I've tried all sorts of materials, strand counts, etc. over the past 20+ years and to date the best for me is 18-20 strands of BCY-X (about the same size as 12 strands of Dynaflight '97).
Like I say on the FAQ section of my site though...do your own experimenting to see what works best for you.
Chad