500 hp at the wheels is a whole hell of a lot of power. Making that much power means redoing basically every system in the car. Otherwise it's no different than making a WRX get to 600ish horsepower too. More importantly, the car wil become extremely one-dimensional. Well, two if you count dyno ownage.
But forget about road racing or autocross with a turbo that big.
Edit: As this is my 555th post, I am no longer permitted to post further, so you'll have to get details from the rest.
555! w00t!