A bit too big, IMO
I agree with you on data but have to disagree on method. Spoiler does not add HP therefore dyno data is useless. It adds down force by having lunches on top of the spoiler so data should be more like how many Wopper it will fit /w drink or pints. This may not be definitive method so perhaps others can chime in.This thread is useless without data.
Put the car on the dyno, and lets see how much HP the spoiler added