I compared the full-zip version of this jacket to OR's Helium II, which weighs 6.4 ounces in a size large. It too uses Pertex Shield+ DS 2.5L fabric.
While searching for reviews online to compare the two (Dave C has one here) I found the OR Helium II on sale for $50, so it was a no brainer. My biggest concern was going to be the fit in the body and arms since prior OR clothing has been a bit baggy, but I was happy to find that the Helium II has a more athletic fit.
I've only had it out in winter conditions (snow) so no real test on how water resistant/proof it is. As far as breathability goes, well just like every other WPB jacket you'll appreciate the front full length zipper to cool off when you over heat. The fabric does feel much softer and drapes better than any other WPB shell I've owned.