Scott, the lighter sail cloth will take shape better (sooner) in light air, but get blown out faster in heavy air. And vice-versa, the heavier cloth will hold shape better in heavy air, but probably be harder to fill in real light air. And with a smaller boat, the lighter cloth might be all you need.
You might ask both lofts what weight they reccommend for your size, in the wind range that's more common in your area. SF bay sailors might target 25 knots, where LI Sound deals more with *2* knots in the summer.
Used sails are *often* blown out, and while they may work well enough to get you started, simply getting new ones that have all their shape and power available to you can really be a treat.