I don't race the car, but I do like having every ounce of performance for the street (if I went to the track a lot, I would likely run 285/35R18s all around). I would never put heavier 20 inch wheels on my car...I can't justify more money, less performance, and likely a harsher ride. I certainly don't think the stock 19s look too small. I haven't made up my mind yet whether or not 18s would look too small or not. Look at the E63 AMG though...it rides stock on 18s, and AMG division knows what they are doing.