[aerohead]

Bugatti,Buick,Ford,GM,Jaguar,Lincoln,McLaren,Mitsu bishi,Porsche,Renault,Subaru,and Tesla have,or are now using active suspension to lower their cars at speed,or have reported drag benefits from lowering.
Sometimes,the inclination of the vehicle was modified for optimum drag characteristics while on the highway.
Technically,you'd have to dial the car in in a wind tunnel,in order to achieve the best results.There is no 'shoot-from-the-hip' rule of thumb to go by,and vehicles will vary on a case-specific basis.
If you presume that HONDA optimized the Civic's production inclination already,during development,then you'd want to lower the front and rear by equal amounts.