I build my own strings. 18 strand Brownell B-50 with .015 Brownell mini serving for the end loops and Brownell .020 diamond back for center serving is what my old, less efficient, 1958 KS likes. BJ nocks fit perfectly. I get little or no stretch after about 100 shots. I set my brace height at 7-5/8" and after about 2,000 shots it settles at 7-1/2". String stretch is largely a layup issue. Nock fit is largely a choice of center serving and/or nock.
I've tried 12-strand, 14-strand, and 16-strand B-50 but there is no speed advantage according to my chronograph. There is much more noise with the lesser strand strings.
I'd be interested in the B-55 results, number of strands for bow specs, servings used, and if there were any speed advantages and what if any noise issues there are compared to the old standby B-50.