I was looking for a pack back in December. I too am tall, 6'4". Every pack I tried was too small.
I ordered the Burton Zoom pack and it was way too small. So I did more research and ordered the Dakine Poacher: http://www.dakine.com/snowboard/packs/snow/poacher/
and the Dakine Camera Block.
The Dakine Poacher fits great. And it carries a lot of stuff: my 5D, 17-40mm, 100mm macro, 70-200 L, and 400mm 5.6, 580 EX, 550 EX, and an IR converted Digital Rebel, plus filters, gloves and light jacket + a water bottle. I strap my Bogen 3021 to the outside (or a monopod would also fit).
The access is from the back and the top. So if you take off the pack, unzip the access cover to gain entry to the camera block. Not everything will fit in the Camera Block but there is room on top of it for storage and access from the top of the pack. I typically place lenses in the camera block and flashes and bodies on top in protective cases. The nice thing about access from the back
is that the part of the pack that goes against you stays clean.
The pack has an internal frame, waist belt and chest belt. I usually place a light jacket under the Camera Block in the bottom of the pack. The Camera Block fits real snug in the back back. Nothing about the pack says camera equipment inside, unless a strapped on tripod gives it away.