My currnt backpack a Kelty 3000 wieghts in at 74 oz and the website says 3000CI. In looking for a lower wieght pack I have noticed that all of the internal frame packs in the 3000CI size range do not look like I could fit the same amount of "Stuff" in/on them. I attach 2 compression bags on the external part of the fame with volumes of 10 LT (600CI) each. So am I correct that I need to look for a 4500CI+ internal frame pack to achieve the same carring capacity? If that is true do you realy save any wieght by switching to an internal frame pack or is that more of a comfort thing?