for me, a low strand count ("skinny") bowstring isn't about a "performance boost" (arrow speed), it's about a quieter and perhaps more efficient modern hmpe bowstring. lots depends on the bow and the archer. there is no way to know what any bowstring will do for any bow, any arrows, or any archer, unless the archer invests the time and money in personal testing.
in building a low strand count bowstring, the string loops must be padded - this is true for either flemish or endless bowstrings, but more important for flemish since the loops on that string type aren't served.
why some folks think or say that a "skinny string" will hurt their fingers is beyond my understanding. all bowstrings need to have an appropriate center serving diameter to fit their arrows' nocks. with a low strand count bowstring, this will mean either increasing the serving thread diameter, or padding the center serving area, or both. the result will always be a center serving diameter that will feel the same to yer string fingers as your fatter bowstring has always felt to ya.
down to brass tacks, for me the advantage of a low strand count bowstring is a tad more "spring to the string". imo, less strands of uber non-stretch/creep hmpe will make for a "softer" string on release. this is just easier on the stick bow limbs, and this has always been my perception with low strand count strings, and i have built them for decades.
since most all hmpe (High Modulus PolyEthylene) fibers (pick a brand - dynaflight, fast flight, 450+, D10, F8125, whatever), will break in excess of 100#, it's easy to see how an 8 strand hmpe bowstring will have greater than 800# of tensile strength - far more than needed for any 70# stick bow, let alone a 50# bow.
i'm not advocating or dissing "skinny strings". only you can tell whether or not they're worth using with a particular stick bow. just another tackle variable to think about ... or not.