let me save you allot of research, if you want a lightweight rucksack, with a breathable off the back backsystem with frame and 58 litres of storage will cover you, then look no further than the osprey exos 58 rucksack, weighing in at at 1.14 kg it is the best rucksack money can buy with its feature set.

I prefer the green version but your preference

http://www.ospreypacks.com/en/product/superlight/exos_58