I should preface my comments by saying I am not a pure climber by any means, but an alpinist who enjoys tackling the numerous 4000m peaks in the Swiss Alps. I generally take a very light rack, 35L backpack (Blackdiamond ice climbing pack) and move quickly. I often take a 12x zoom digicam, simply because it's small, light and I'm not too worried about loosing it.
Like you I have struggled with what pack to use when taking a DSLR setup. I have two setups depending on situation e.g. number of pitches necessary and complexity.
1. The Lowepro Photorunner is quite good imo but it's not going to handle a quality 70-200 2.8 lens. The Nikor 17-55 2.8 DX (If you don't know it, it's a physically big and heavy lens) fit's well in the bag when mounted to a D200. The compression and belt straps do a good job of keeping it stable even with a small Gizo attached.
http://lowepro.com/Products/Beltpacks/clas...oto_Runner.aspx If you need more lens space either a separate sliplock lens case or an Off Trail from Lowepro would work.
The issue I have is that belt packs in general just get in the way of my rack. I have suspended it on a cord or sling but I'm not sure I'm totally confident with the protection offered in this scenario. I recently picked up a general photo backpack from
http://www.kata-bags.com/index.asp which is very tough (they also make bullet proof vests). One of their beltpacks would offer more protection.
2. I ditch my 35l climbing pack for a 45 and stick in a toploader from Lowepro and a lens case for a larger or wider lens. I can clip it to the outside of the pack if I want to have quick access otherwise it stays in the pack. This is what I do when things are a little more difficult or hazardous. The camera is less accessible but more secure. I climb with a pack a lot and find this solution does not obscure my rack as much as the belt pack.