Joined: Aug 2008
Posts: 13,140
Likes: 2,162
From: Ann Arbor, MI
Bikes: 15 Kinesis Racelight 4S, 76 Motebecane Gran Jubilée, 17 Dedacciai Gladiatore2, 12 Breezer Venturi, 09 Dahon Mariner, 12 Mercier Nano, 95 DeKerf Team SL, 19 Tern Rally, 21 Breezer Doppler Cafe+, 19 T-Lab X3, 91 Serotta CII, 23 3T Strada
There are a few variables the OP didn't control for, e.g. the type of backpack shape (some are quite square and carry weight up high on the back, others are sloped and carry weight lower), how the load is carried on the rack (pannier or trunk), and if pannier, size, type, and single or double. All of these would make a difference, I'm sure. Or how about my setup, with a seatpost mounted Xootr Crossrack which tucks a pannier perpendicular to the bike behind the thighs and up against the butt?
All that being said, my guess would be the right trunk pack is fastest, followed by the right backpack, then Xootr, then dual panniers.
I'm not aware of any studies, but would be interested to know if this question has been tested, too!