Take a look at the Lowepro TLZ Mini, TLZ 1, or TLZ 2 (Top Load Zoom). What size you need will depend on the length of your lens. These are lighter than your other choices. Most packs will have webbing, if not a daisy chain, running over the padding which you can clip a carabiner through. I prefer the Nite-ize s-biner as they are light, cheap, have a good gate, and are available in many sizes. The size #3 is a good fit for most webbing on shoulder straps.
Check out the thread "Full Size DSLR on the Trail" for some pictures.