12 strands is plenty strong. Dyna '97 is 125# test per strand--I've used a 12 strand on 70+# bows. I prefer 14 or 15, just because it seems to be a bit quieter and works out best to fit my nocks. You can go with a good bit less--Shrew bows come with a 6 strand 450+ (450+ is 155# test per strand), but I don't see any real advantage to using a tiny string.

Chad

Long Bows Rule!