The car isn't nose heavy. It is just set up with too much under steer (Mercedes has no way of know what kind of idiots are going to drive their cars). A stiffer rear sway bar will loosen the car up. The engine will not run just fine on regular gas. It will just run. The computer will adjust to the fuel by retarding the ignition which will result in less power and mileage. I know this for a fact. 10.5:1 is approaching the limits of pump gas, especially in hot weather. Got a problem with a V8?