No wind tunnel testing needed. The more in line your bags are with your bike and body, the better. If you look at frontal area, there is really no additional exposure from a handlebar bag, frame bag, saddle bag, backpack (unless you are in the drops) or trunk bag. As wind angle increases, that is less true. The worst for aerodynamics are panniers, either front or rear, because they are almost completely exposed to the wind. The larger the pannier, the greater the resistance, regardless of location.

This is a fairly decent aerodynamic setup. The handlebar roll is exposed to the wind (need to make it narrower), but the legs and other bags are in the slipstream.