It really depends on personal preferences and physical ability. Are you standing in slow moving lines for a longer duration? Is your back, core, knees, and/or pelvis in good condition? Are you at least average size and weight? If you fly carriers which will weigh & size carry-ons and personal items, it can be very frustrating to have to check a one bag due to it being overweight or start pulling things out to wear them through the bag check. Most people will need to optimize their contents if carrying a 35-40L bag and want to be under 7kg including laptop https://www.reddit.com/r/onebag/comm...ically_travel/ If you haven't delved into optimizing contents as part of one-bagging, just be aware that it can be the costlier way to optimize weight. New bag to shave 1 lb = $200-300. New ultralight laptop/surface to shave 1 lb = $400-1000+. New phone to leave laptop and camera at home = $600+ (excellent weight savings, though).

I don't see a reason to rule out Peak Designs if you can handle the pack & content weight without having regrets and benefit from the alternative organization options. To be fair, different bags & suspensions also carry differently so it could carry a lot more comfortably than a similar volume bag at a lighter weight. I hear Tortuga put a lot of their weight penalties into the straps, belts, framing, and back padding so it carries more comfortably. Then again, if you can live off 20L for a few days, 30-35L might do just fine and may even fit under some airline seats if there's not enough overhead bin space.

As others have noted, each person's onebag holy grail wishlist will differ. I'm pretty sure none of us wished for a heavier bag.