If you are anything like me with camera bags, every one is the best thing ever for about 2 weeks, then... But that is a lot of gear for a backpack, I am always happy with lowepro as far as build quality and ease of use goes. Having said that I recently bought a thinkTank sling 30, which I had to modify inside with some lowpro dividers but holds 2 full frame bodies, 70-200, 16-35, both attached to bodies, and 50 + 24 pc-e loose, plus filters, cards etc. not sure if you make hold 4 bodies tho. Great for in the city, and also has a tripod pouch. I have backpacks but just use them for hauling gear to location. I find them to slow to use when walking around shooting.
However, I did see that lowepro have released a range of backpacks that spin around so you can access them without taking them off/putting them down, but I don't think they hold anywhere near that amount of gear.
Let me know if you find what you're looking for!!!