Peter, it is just as much a question of scantlings as of choice of material. The battens Annie describes seemed to bend too much in everyday use, so then it is no surprise that they broke in a storm.
If your battens don't bend in a breeze, they should be fine, but if one or 2 of them, for instance the two in the top, show signs of pumping in F4, it is a good idea to replace them or add a couple of layers of grp on them.
I have found that as the wind picks up and I reef down to 4 panels or beyond, the remaining battens get so much support from the lee topping lift that they seem to fare better than when 6-up under full load.
Arne