Their backpacks are nice- but I've never really been fond of using a true backpack for mobile photography. I have a cheapo Caselogic sling that I still use (broke the poorly attached waist strap), that has carried a 60D with 15-85 and now a 6D with 24-105L (the L lens is larger by a good margin). I still have room for filter/flash card/battery holders, my 70-300 lens, and a few primes, though it's a tight squeeze.
Looking at Kata's site, I'd be pretty interested in their Orbit 130
messenger-style bag, given that it can be carried like the sling or like a typical shoulder bag, can handle larger lenses, and can handle a laptop or tablet.