I went to my closest REI this morning to check out the Osprey Porters (30, 46). The 46 was just too big (I am a 5'4" female) and the 30 was too fussy. All the laptop compartment padding, on both sides, took up depth space from the main section. While the straight jacket wings do their job, it was just too much fussy bag and not enough actual packing space for my use. I ended up getting the Osprey Nebula 34. It's not as decked out: the waist strap is just a strap, no padded wings, and the straps don't have a tuck away zippered pouch, but it is very light (2 lbs 1.5 oz), it has external cinch straps, and I think it may well fit underseat if not stuffed to the hilt. I did a test pack at home and it held two ebags medium packing cubes packed full plus two ebags slim cubes, also packed full. This was just in the main section and there was room for more. Since it is likely that I will be using the backpack straps rather than a shoulder strap, I think this is a good compromise for me. I do wish Red Oxx could figure out a way to reduce the weight of their Sky Train to a 2 or 2.5 lb range. I am a big Red Oxx fan and feel like a bit of a traitor buying an Osprey.

Am still curious to read your reviews on the two sizes of Osprey Porters.