I use the 3.25 all the time. I would double layer it on the deck but mainly for strength on doing re-entries. I use it single layer on light lay ups just fine. It is extremely thin stuff. You have to be graceful with it when laying it out. It is a dream to wet out. The weave is so smooth it needs little to fill it. Just one fill coat and if you are good and do that as a hot coat with a squeegee you only need light sanding for the varnish to adhere but not to smooth it out.

2x 3.25 oz gives you a 6.5 oz layup with the strength of a much heavier cloth but the weight of a lighter cloth.