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I've used a Carradice twice in TCR. It's heavy, with a Bagman and probably less aero, though Barley isn't that big. Doesn't sway even if it isn't tightly packed, easy and quick access and easy to keep things organised in it, with the pockets and all.
Barley could still be pretty aero. I think aero becomes an issue for the wider ones which stick out past your hips. Either way, it didn't stop you riding pretty fast!
Is a Carradice a very bad choice? I am put off the Apidura type bags for all the reasons listed above.