I usually run with a car built/adjusted to be within 1 second (+/-) of the pole.
It's odd, but I am very reluctant to add parts to my race cars. I play with all the settings that are already adjustable, but I rarely buy more parts. I want the experience of racing the purpose-built cars as they were built. It's just a strange prejudice of mine, I guess.
I have street cars running the gamut from +150,000-credit buildups to bone stock. I do tend to add parts only as needed there - addressing the weaknesses by priority rather than just shooting the wad at one time.