Go to www.photobackpacker.com. I have their RPT P1 and the right cases for my gear and it's just awesome. At maximum load, I carry a Tachihara 4x5, 3 lenses, a Rolleiflex 2.8F TLR, a Nikon F100 with a medium zoom lens and a 180mm fixed lens, a Pentax spotmeter, quickloads, tripod and all the other related odds and ends I need. I usually leave the 35mm stuff at home, which leaves a little more space in the pack and keeps the weight down. By the way, this pack is way lighter than anything from Lowepro and the suspension is top notch for extended hiking. Hiked around in Death Valley for a week recently and can't think of a better way to do it. If you're just going to carry the 4x5, you could certainly get away with their smaller backpacks. If you're shooting 5x7, 8x10, or multiple kits like I am (or if you're going to pack for longer hiking), then I would only consider the P1.
I have no connection to the company, just very happy with the quality of their gear and highly recommend it to others. Oh, and if you're thinking about not getting their cases because they're expensive, I'd think again, because they're probably the best part of the system. Great protection and well designed for easy but secure access. Ok, I'll stop the infomercial now. Best of luck.