I never heard that about the pistol weight. Steel ammo is crap. I try not to buy any but it is tempting due to cost.
I found some reports that say the weight difference is 3 ounces in the upper.
My gwacs lower is 10 ounces lighter. I think I am as light as I am gonna get it. Not that it couldn't be lighter but any further gains will not be worth the trouble and cost. I am gonna cut the front sight off. I looked at some other "shaved" gas blocks but the cost of a new sight is only 35 bucks if I every want to convert it back.