[JeremyD]

One variable not mentioned here - but deserves some merit is the weight of the car.

If you have a #3000 car or even #3200 with you in it (and yes, there are some Carreras, 964's and 993's that approach, if not exceed these numbers) then the spoiler effect will have much less impact.

For example - @3000 lbs - negating lift by 300# (assuming 40/60 weight distribution) #1800 on the rear axle - Without a spoiler - you get 16% lift. With duck - you reduce that to #150 or 8.3% =

But if you are at 2500 lbs = same numbers - you effect the lift with a spoiler by 20% and 10% with a duck.

So - from a percentage basis - the more you reduce weight - it becomes even more important to get your aero ducks in line.