I have always run 10w30 Mobil 1 in the high compression NATTs. Still no issues on the original ConverTT (6th season now) and I have been flogging her on the track this year.
That being said, our ambient temps are more like 65 to 75 so arbuably 10w30 is on the heavy side up here. I am from the "thicker is better" camp - if I was going to track in the South with my configuration I would definitely swith to 20w50. IMHO