I've just won the Indy 500! That race is intense, I've done the 24 hour races at Nurburgring and Le Mans on Gran Turismo but they're not as hard as Indy, you're constantly concentrating on not hitting the car into the wall, one mistake and you can lose 5 laps or take the car out of the race entirely, you can't even rest on the straights because with the car setup they're a constant right turn to keep out of the wall.
I turned the difficulty down slightly to give a little more room for comfort when lapping cars, this wasn't my first attempt (lots of crashes and a 4th place after 199 laps) and I learnt a few times that a late dive down the inside is not very smart!