I was told by the sellers of the biax to expect about a 30% increase in strength when going to biax from the same weight woven. I chose to go with 12 oz biax vs. 9 oz woven. Based on the following:
"Directional fabrics ( biaxials, triaxials) are much stronger while lighter than the common woven fabrics. They cost more by the area but almost the same by weight. As they use less resin (less weight), the resulting composite does not cost more than the low tech one." I also found the biax much easier to work with. It conforms to shapes and corners much, much, easier. The end result was a stiffer, stronger boat at about the same price.
Paul