For me, 500 has always been about the limit for the street....and even at that level it's a rare experience that you can actually get it all hooked up.

With street cars normally being around 3000-3500 pounds, I usually build for torque to be at the 450 level at the wheels, run the suspension "loose" to get the best weight transfer possible, and lay off the deep gears so the tires have a chance to stay hooked. I've found that 450 ft. lbs. of torque at the wheels in a 3200 pound car with a gear ratio in the 3.50-3.73 range will allow the car to work on the street. Guess it would also depend on whether you are shooting for driveability or outlandish!!!!!!!