If you go as light as possible, you'll need less pack. If you take the five pound two person dome tent, the synthetic bag, the thick inflatable sleeping pad, etc., you will need a big heavy-ish pack to haul it in.

And then there's the matter of a pack fitting me that doesn't necessarily work for you. Osprey packs for example tends to work for some people but not all. I hate the frames on them, because the frame hates me - makes me gimpy, limpy and sore. You might find it the most comfortable pack in the world. It Just Depends.(tm)

Try on some packs with weight in them, or find a store that will let you bring your gear in and find a pack that it'll fit in.