The Carradice Super Cs are listed as 875g each, so 1750g or 3.9 lbs. for the pair. So yes, they're lighter but not by a lot. It seems to me that right around 4 lbs. is typical for full size rear panniers.

For commuting I generally only used a single pannier and just put my things directly into it (i.e. no backpack or other bag). But if you're using the pannier to carry a backpack then the weight of the packaging starts adding up. For that application I modified my backpack by adding the bike rack hooks used by Lone Peak for their panniers to the corners of the pack. So I just hang the backpack on the side of my rack which leaves the rack top free in case I want to stop and do some shopping or have anything else to carry.