I think 525 is perfect. My LS1 is putting 406 to the wheels. Its mini tubbed w/335 tires. Its spins them pretty easily from roll in 2nd gear. I dont have super sticky tires, but at some point traction becomes an issue. A well tuned suspension will help with that, but for how you describe you'll be using the car I think you'll be happy with 525- probably 450ish to the tires. I have no knowledge on the 4L70, as I have never run one. Down the road if you felt like you needed a bit more, you could do a cam swap & pick up a few more HP. I am not familiar with the cam specs on that motor, just speculating. If you are talking open track- like full road course, that may alter your decision a bit. Keep us posted on your progress.