I have done a good bit of backpacking where weight is even more important. Awhile back I purchased

• Zpacks duplex tent with poles and stakes - this comes in at 25oz total and packs very small
• Katbatic down quilt instead of a sleeping bag - 26oz and it stuffs very small
• Thermarest NeoAir Xlite pad - 16oz and it rolls pretty small

My best bet would be to load my Ortlieb's with everything I will be carrying and see if it all fits. The new Trek 520 comes with rear and front racks. If I can get by without front panniers I can take off the front rack and save even more weight. I do like the idea of some type of drybag in the 15 to 20 liter range for the top of the back rack than can be loaded with food