The 4mil X-ply monofilm is what we use for the window in the Isotope Jib (which is not battened). We stopped using it in panels at the luff of the sail, where furling was really hard on the material, but it holds up as well as the 2mil Pentex on the back half of the sail. I think it would be more than adequate for an Aquacat sail.

I hope that helps,
Eric