They are generally well-made packs. I think most veterans here would recommend that you buy the pack that fits--that's the key element. There are lots of packs that work, but only if you are really comfortable wearing them.

A forty liter pack will be able to carry just about anything you can fit into it--because 40 liters is pretty small. By the time you get a sleeping bag and a tent in there, you won't have room for a lot of heavy stuff. I'd think 30 pounds is a lot for this pack, but it would be hard to get 30 pounds INTO it, unless you are carrying bricks.