My Vette made 700 (15k miles boosted) and I felt it was perfect for a street car! Drove mostly like stock or I could roast the tires at 70 in 3rd! But even at 600 it was faster than almost everything in the street!
That being said I think anything over 800 is out of dd range and more parts break! That and at that level you better do the internals too!
500=fun car
700=fast car
800+= both and more money and down time but INSANELY fast car!!