Has anyony had any experience with the Conti tires coming stock on the xfire? Dealer charged for the tire upgrade, Z rated tires, checked the Conti website and Tire Rack for opinions. Conti does not indicate the tire as a Z rated tire, Tire Rack users indicate the tire is noisy and wears out quickly. Since the car is 2 days old, should I 'opt for the Michelins? Dealer says they'll switch without questions. Thanks for the quick response in advance. Great site. James. :P