I've driven the 135i but I really like my 128i vert. I agree the power is more than adequate and is even enough for an autocross - light track use. You have to keep the rpm up to keep it moving quickly but that is how I think cars should be. The 135i has lots of torque at much lower rpm so being in the right gear is not nearly so critical to fast movement. Nice but could make you sloppy. The difference in power does not seem like it's of practical use on the street.