I'd agree with what the other two said. However, also take a look at the Osprey Volt 60 and Volt 75 (whichever will hold your gear - take your gear with you and load it up; don't trust sandbags, as they distribute wieght differently.) In my opinion, they are far superior to the Atmos Series pack, and handle weight much better. They're also much easier to get the fit right. The new Atmos AG series can be a little finicky to adjust properly - and if you don't, the thing hangs on your back like a tired three-year-old.
Much as I like the looks of the Atmos and had a discount to apply to one, I could not get it to sit right on me with several fittings and adjustments. I gave up and decided it was OK, but not an improvement on what I already have. Love the line about the tired 3 year old! Couldn't agree more with all said above. Fit is it.