If you ask me, the difference between an auto and stick is purely a question of fun. Sure auto's slush box eats a few HP, and yet they are more consistent in high HP braket racers. And there probably is a few % difference in dyno measured power and maybe a few tenths at the 1/4.
But all that is fairly minor. To me a sports car should have a few important elements, namely, a stout nice sounding motor, a good suspension, and above all a stick. To others the stick aint so important. To each his own on this. But for me, it HAS to have a stick.