I'm up against the same question. I do have a Think Tank Rotation 360 that I like for my everyday bag but I didn't consider it last summer when I was shooting and hiking in the Alps. It's just too heavy. I used an older LowePro trekker and didn't bring big glass because I didn't need it. Remember to factor in a couple liters of water and some clothing layers to your total weight too. Moose Peterson has done some thinking on the subject that you might want to read, here is the URL
What's in Moose's Camera Bag