Go with the JB4. Using the CANflap option will change your exhaust sound and give you a good kick in the pants when you step on it .... with a totally stock exhaust.
The JB4 is probably the best per dollar up grade you an make to the 335I. A good set of tires cost more and have a finite life.
No matter how fast I go, there's always someone slower in front of me.
JB4 PNP .... Love at every stomp on the go pedal!