lol, it's funny that you guys mention this. I just picked the game up last week. I was at 11%. I just beat it last night.

What I did was, I did a bunch of little shit till I got to 25% completion. Then I entered the Camaro LM Race car with all the upgrades done to it and Super Hard racing tires into the 24 Hour Nuremburg Endurance Race. I left that shit on overnight, checking back in every now and then to reset the race speed to x3. After I won I got 1.2 mil credits and the formula 1 car. Then I put the formula 1 car in the Gran Turismo Championship race and beat the game effortlessly. Good times... If only I was skilled enough to do the driving missions to get the Jay Leno Tank Car... My god how I covet that car.