I've got the flipside 400AW and love it, noted as the previous poster said the zips don't go all the way to the bottom, but I only put smaller things in the bottom divider section I have set up. Front pocket on the 400 is big enough to fit plenty of stuff, tripod holder works well for a fair sized manfrotto tripod, i can loosen or tighten the holding strap.
Each side mesh pocket can comfortably hold a 750ml water bottle each.
I find the 400AW pack comfortable for all day wear, its a big pack, but I'm a bigger solidly built guy!!
My advise find a style of pack you like, and try heaps from as many makers as you can. Buying a pack is like buying a bed, take your time and test them out!!
If I can see it, I can shoot it... albeit with varying degress of success.