Now that I've retroactivly answered that, on to the race:
easy race: turbo 2. All your competition is stock, so this will blow them away.
challenge: Depends on your skill level. I think most people should be able to win with just N2O, and you can use it more or less depending on how much you need it. For more of a challenge, add balast and lower the tire grade.
easy max a-spec (I don't think you can get 200): Don't get the 10k special, don't change the oil. Buy a race trans, N2O, light flywheel, and comfort tires. Add max ballast and optimize the gear ratios for the track.