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I love my Mountainsmith TourFX lumbar pack (large waist pack). It's quite comfortable to hike for some distance (much more comfortable than my sling-style bag). And easy to use as a shoulder bag as well. It works fine to carry it in front, but it is really meant to be carried in back, so I usually wear it as a lumbar pack while hiking then undo the waist strap and shift it to the shoulder strap when I get to a location I want to shoot. It is probably bigger than you are needing, I carry a EOS-40D, 17-50/2.8, 30/1.4, 50/1.8, 70-200/4, and flash with room to spare (could easily carry a 24-70 instead of 17-50) - it's tall enough that I can close it with my 70-200/4 mounted.
I don't believe the smaller 'SwiftFX' pack would be able to fit a 70-200/4, and I can imagine anything much smaller would fit a 70-200/2.8. There was a slightly smaller version that they aren't making any more called the 'Day FX' that you may be able to find online that may fit what you are looking for if it is a 70-200/4.