Hi,
Something else you might consider; a non-photo backback "converted" to a photo backpack. I got this idea from someone on a Photo.net forum a year or so ago after getting frustrated with the bulk, weight and bad harnesses of the photo backpacks. I bought, tried and returned a couple of LowePros including Photo Trekker AW and some Tenbas. I'll never try another "photo" backpack again.
I use an Osprey Eclipse 32 daypack (large) with a Pelican 1450 divider replacement set plus some assorted additional dividers/pads and some LowePro S&F pouches.
The Osprey is not a photo-specific backpack, but it is a panel loader, has a very nice harness and "straight-jacket" side panels which are padded much like a photo-specific backpack is padded.
Here's Osprey's URL. They have other and bigger models too. You want a "panel" or "front" loader, not a top loader if you go this route.
http://www.ospreypacks.com/eclipse_32+5.htm
Google on "Pelican cases" or "Pelican case replacement divider set" and you'll find just the divider set; no need to get the entire Pelican case.
It's not custom-built for photographic equipment of course, and each item won't have it's own special padded compartment like a photo backpack, but I think photo backpacks are over-padded, over-weight, and the harnesses often aren't that good. The pelican case insert gives you the compartments for most items, but I still have a few loose items stuffed here and there.
Here's what I can carry in it to give you a feel for what it holds.
It's "packed to the gills" with all this stuff, but it's still pretty comfy.
4x5 Large Format field camera
80mm Schneider Super-Symmar
135mm Rodenstock Sironar-S
300mm Nikkor W
20 Quickloads (film)
Quickload film holder
Dark cloth (spread out and used for additional padding inside).
Pentax digital spotmeter (in Lowepro SF pouch on outside of pack).
2 Loupes.
Cheap reading glasses.
D70 OR F100 (only fits 1 small camera if carrying LF equipment)
Nikkor 80-200
Nikkor 35-70
Nikkor 17-35
Cokin P filiter holders, adapter rings for every lens.
2 Gradual ND filters.
Circular polarizer on each Nikkor lens, plus pola for Cokin P holder
Gitzo 1227 CF tripod (straps on back or sides or I carry it).
GPS (clipped to outside)
Small umbrella
Lightweight nylon cover which also serves as a tarp to lay pack on ground
2 trekking poles (Can stuff them on the sides if not in use).
2 litres of water (on sides).
Power bars, trail mix, etc.
I'm good for about 7 miles and 1500 foot ascent/descent with this, but any more than that and I'd probably not make it. More miles less elevation change perhaps.
It is probably slightly slower to access equipment than a photo-specific backpack because the whole back doesn't "peel away" exposing everything like a photo backpack does. However, for me the most time I spend with a photo backpack is taking the thing off and finding a place to lay on the ground or putting down the nylon cover to prevent it getting muddy/dirty, etc. A few extra seconds digging around doesn't bother me.
Without the large-format equipment, I can easily carry 2 small-format camera bodies (D70 and F100 for example), film, a 90mm macro and 50mm fixed, and I'm pretty well covered, and about 3 pounds lighter. I'm reasonably sure the D2X would fit nicely in place of one of these cameras.
This pack is longer and narrower than most photo backpacks I've tried, which I think makes it more confortable; it hugs your body a little more that way I think.
Anyway, something to think about. You have to be willing to not have everything perfectly compartmentalized, you'll need a few extra pads from various other bags you've purchased and have stopped using, and it's not "one stop shopping" to get it all to work well, but I actually found it kind of fun to pick and choose peices from different vendors that work well together. The various parts you need cost combined about the same as the photo backbacks.
Good luck in finding your "ideal" backpack. Nothing's perfect and it's a never-ending quest I think (which is why I have some 12 camera bags collecting dust).
(hey, I like to mix hobbies!)