Hi I would like to compare the kata 3n1-30 with the lowepro fast pack series, the 200/300
you need to bring all your equipment to the shop and try it
look at the fit, the accessibility, the materials ... ...
trying bags without loads is no no... every bag feels roughly the same without load...
if ask my opinion, the Kata is more comfortable to wear but in the case drop the bag.. the Lowepro will protect the contents better.
the only thing you can do is try them out first.
You wont see me much less remember me but i am the guy who makes you look good.
For a gripped 40D, you'll need the Flipside 300 and not the 200, which would be too shallow.
Personally I'd get the Flipside 300 because it fits your gear perfectly (40D, grip, 17-50, 70-200 f/4, as well as your nikon gear - all on your blog) and leave some space at the top for misc items.
I prefer Think Tank photo bags, but the flipside 300 is one exception where I think lowepro did a novel job.