I have a Cascades (about 4200 c.i.) pack that I used before starting the lightweight/UL thing. It was a heavy pack (around 5.5-6 pounds I want to say?), but it fit me well. I'd guess that for the heavier packs with heavier loads, fit and proper load transfer becomes increasingly important, so I don't know what to tell you besides getting your hands on one and trying it out with your typical load-out.