Need for Speed Heat, Visual Customization

Hello! I have a question regarding the NFS Heat visual customization.  I understand you can change the level of brakes under the "Performance" tab, but I am wondering if when you change out brakes and calipers under the "Customization" tab if it actually makes a difference to how the car performs (like in NSF Payback). 

I cannot tell any difference in how the Ford Mustang brakes when I changed it to SpeedHunter and Brembo parts.  So...is it just eye-candy or does it make a difference.  And as far as that goes, what about the spoiler, splitter and diffuser?  Same question.

Thanks!