To turn the 535i into a powerful beast, but also keep it daily driveable I would suggest the following
1. Tune - You will fall in love with the additional power, it really transforms the car. It will pull like a torquey large displacement V-8
2. Suspension - Depending on your preference, a Sport or Race spring to improve the handling of the car. You should also consider shocks if you go super low. The stock shocks have a tendency to give a harsh ride when coupled with a more aggressive drop.
3. Get rid of the runflats. Couple this with a lighter weight rim and you should see a noticeable decrease in stopping time and acceleration, as well as improved ride quality and handling (Tire mobility kit is recommended if you are ditching the runflats).
4. Exhaust - The N55 engine responds really well to a down pipe. You will see substantial HP gains doing this, as well as an improvement in sound. You can also consider a cat back for more sound. I'd recommend a resonated downpipe if you go that route so you don't get the raspy drone, which is definitely not desirable in a classy car like the 535i
5. A great pair of polarized sunglasses, nice driving shoes and a long windy road.
