For years, Ferrari and McLaren have battled each other in the rarefied air of Formula 1 racing, but increasingly they have taken that competition to the street, now that the U.K.-based McLaren has begun a serious road-car program. The ultimate expression of this competition came at the Geneva Motor Show, where Ferrari unveiled its replacement for the Enzo, called the LaFerrari, and McLaren brought a production-ready version of its supercar, the P1, which made its concept debut in the fall at Paris. It is going…