It is exactly the same as the R6. It was given a special name for Spec Miata racers to get a more competitive price. I don't know if you can get the deal if you're not racing SM, but it's worth a try.
Stay away from the R888's. They do not last and can't make a thirty minute race before getting very greasy. SM had chosen them as the required tire for 2009, but has just returned to the RA1's because of all the problems.