OR makes a lighter rain jacket called the Helium II, which uses Pertex instead of GoreTex; I've never used Pertex, so I can't tell you much about it. I've seen others on this site praise it, though. The jacket weighs 6 ounces, and REI carries it (though iI didn't check for in-store availability - could you have it shipped to the store, and return it on the spot with no shipping charge?)

Besides REI, is there a local independent shop near you? If so, they might carry OR.

Hmmm... maybe I need to visit them tomorrow on my way to the trailhead, and take a look at the Helium stuff....