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Guys, give a look at the OpTech sling strap linked in the 2nd post above. I use this setup with heavy lenses at airshows, and it allows the weight to balance my rig perfectly when it hangs at my side, ie a 100-400 attached to a 40D will hang parallel to my waist when I want to free up my hands for something or rest my shoulder.
What I've done is bought several pairs of the quick-connect clips, as they're fairly inexpensive. The RRS lens plates on both my 100-400 and 70-200 lenses each have 2 small holes at the end of the plates. I have threaded the pig tail of a quick connect through both of those holes, on both lens plates. So, whether I'm using the 100-400 or the 70-200, the lens/camera setup is attached securely with two clips, so I have a built in backup in case one clip should fail. Having two clips instead of one also keeps the rig from spinning when hanging at my side. I don't use the sling for a body and smaller lens combo, but it would be easy enough to put one clip on each of the strap lugs on the camera body if I wanted to.