Suggestion:
Go easy on a good sleeping bag. The ultralight down bags tend to be constructed with very light fabric baffles which enhance the lofting effect. If you get rough while jamming it in a stuff bag you can possibly tear things internally. I've seen guys jam them in very roughly and it's not the way to go. I like the Granite Gear and Sea-To-Summit compression bags. Push a good down bag into it and then evenly compress with the cords or straps. The best eVent bags are absolutely watertight and can be carried externally if needed. I have no problem leaving my bag on the top or bottom. I most recently placed it on top of my loaded pack and cinched it down with top straps.