I highly recommend the Blackrapid RS-4. I find that it works very well for hiking, which I do quite frequently with my 7D + 100-400mm. The camera hangs at my side with the lens extending behind my back (I attach the strap to the tripod ring), and grabbing it for a shot is easy and fast. The weight is on the shoulder, so it's a lot more comfortable to carry. I can wear it over a backpack (e.g. Lowepro Flipside 400AW). I also like that unlike a neck strap, it can be easily detached from the camera (I use E1 handstraps on both bodies, and when not around the neck I always found the neck strap got in the way). The little zip pocket on the RS-4 holds two CF cards in their cases.
Not sure what support system you use, but I use Manfrotto (tripod and monopod), and I connect the RS-4 with the FastenR T1 (replaces the D-ring on the Manfrotto QR plate), which makes it easy to disconnect the strap and attach the camera to a monopod or tripod. If you use Arca-type plates, I think they have a second 1/4"-20 hole which you can use for the regular FastenR.