Sandy, seems to me that I heard that racing
oil does not have nearly the additives that regular road
oil has. Considering that, I'd be more inclined to change it every 2000-3000 miles max, with normal highway miles. More ofter if you were to thrash the car on the track or strip. Some of the other recommendations are probably just as valid but seems like most of them live in climates with much more humidity and cold temperatures than what we have here in the beautiful AZ Desert.