It also depends on the weight of the bow. Six strands on my 46 pretty much stay put. Six strands on my 52 creep like crazy, but I put an eight strand continuous loop d97 on in and it seems to stay put pretty well so far.
While the skinny six strand my have enough strength to be shot in a 50 plus pound bow, my experience has been that it will creep excessively. While the skinny strings do have some advantages, there seems to be a point of diminishing returns. Creep soon results in an over-twisted string if the bow is too heavy. Exactly how many strands per pound of bow weight is still open to conjecture. It seems to be somewhere around 7.5 to 8 pounds per strand. It may be somewhat less for a Flemish twist string. My experience has been that they creep just a bit more.