M@TTY
There was some comparative testing between the "Egg Brake" and a center pull brake on the front by Tom A. The Egg Brake actually had a lower Cda than the center pull that was tested (not an AX per se), but that difference was well within the variation of the test. I cannot say with statistical certainty which had lower drag, but this does shoe that a side pull brake can have similar drag performance to a conventional center pull, and possibly better.

One overlooked aspect of the brake design with respect to aerodynamics is the separation between the brake arms, the fork, and the tire. The tire creates much turbulence and the gap between the brake arms and the fork should be eliminated. Shimano addressed this with the AX brakes by having the brake arms extend all the way back to the fork. I tried to mimic this affect by making the trailing edge of the brake extend back to the fork with a thin shell of aluminum.

Another improvement is to get rid of all of the edges. Bicycle brakes tend to have many kooks and crannies, but you general do not see aerodynamic things like airplanes or cars with all of the springs, bolts, and pivots exposed.