Finally - a response dealing with wind drag, the overcoming of which which uses up at least half your pedaling power on flat ground. I also have thought for some time that a BOB would be more aerodynamic since it sits behind the bike/rider. Panniers are definitely not - they stick out (and often have random things strapped onto them), especially low rider fronts, which add even more to your frontal area. But a loaded BOB, while aerodynamic, also carries a bit more of a penalty in weight than most panniers, so yeah, it would probably feel even more slow on hills due to the contrast. I've never used a trailer so this is very interesting to me.