I've no idea if there are studies, but I can tell you since I bought a basket and started just putting my backpack in the basket life has been so much easier than riding with the backpack on. Much easier on my back, too after each 13 mile ride.

I feel faster since doing that, but that could also be just because I was riding with the backpack in the beginning and have gotten faster in general from being in better shape.

Edit: I should point out I don't normally carry a laptop, so the backpack's just carrying clothes food and tools. If I have to carry a laptop, I put it on my back to protect the laptop more from the bumps.