[aerohead]

For low drag I recommend that you investigate the roofline of the late-1984 Porsche 962 sports prototype racing car, and 1996 Porsche 911 GT1, both by Norbert Singer, head of Porsche Racing.
This roofline is what aerodynamicist, Dr. Hermann Burst recommended as the 'solution' for the 1972 Porsche 911 Carrera RS 2.7, but was shot down by Harm Lagaaij, head of Porsche Design because it didn't satisfy the 'look' of Ferry 'Butzi' Porsche- III ( designer of the 911 ) 'falling tail line' of 1959-60.