Hm, I'm confused now.
As far as I knew, retarding the timing will hurt performance. However, because the computer usually enriches the mixture at WOT in N/A applications, I'm going to guess that the performance will be hurt mostly at part throttle acceleration and cruising. Of course, my only knowledge of superchargers is that it compresses the air to get more air flowing through the engine, thereby increasing power.
Basically, I won't mind getting something with a supercharger on it as long as it doesn't knock itself to death on 87 octane.