Chris Hu said:
I'm pretty sure Forza 4 is structured similar to Forza 3 and since most races are limited to one class or type of car there is no car in FM4 that can be used as much to win races like the Red Bull Racing Car in GT5. You can use the Red Bull Racing car in a lot more races besides Endurance races you can use it in the Sunday Cup, Clubman Cup, Gran Turismo World Championship, Tuned Car Championship, Turbo Challenge, Japanese Championship, Gran Turismo All Stars, Pholphony Digital Cup, Like The Wind, Super Car GT, and Dreamcar Championship.
Sorry but it's impossible to have the X1 in this races.
And Forza 4 is not like Forza 3... you can use a car below the race class and win easly just using it... so you don't need another car.
Edit - You got the X1 via gift is another option.