Bicycle Quarterly did some wind tunnel testing a while back. IIRC they found little penalty for a front bag because a front bag typically adds little if any frontal area. Large saddlebags added more drag because they tend to stick out to the sides, which
does add to frontal area. All bags add drag in quartering headwinds, because they significantly add to the area the wind "sees".
I would very much like to see pictures once you have attached your bag to your aero bars.
