What CR do black top 20v have from standard? If it is 11:1 or close to it, I agree that you should just use stock pistons. But there are plenty of people with 12:1 on 98 octane fuel. As long as the tuner knows what he is doing there should be no problems. What model Microtech? I have been told by a few experienced tuners that they aren't the best for cars with wit ITBs as the resolution isn't good enough at low load/light throttle.