Road&Track has the ultimate comparison between the Audi R8 Grand-Am, the Audi R8 GT, the Audi R8 5.2 quattro, the Audi R8 5.2 quattro Spyder , the Audi R8 4.2 quattro and the Audi R8 4.2 quattro Spyder . Awesome! For this track skirmish, we're pitting the fastest production Audi, the 560-bhp R8 GT, against...
