In my first race I'm going to run ITE because the car is legal as is.   STU has the advantage of being a national class and seems to be populated by Miatas but they can have significantly more power in STU trim.  It was unclear whether the S2k was legal for STU competition and I posted a thread about it: http://www.sccaforums.com/forums/forumid/35/threadid/399761/scope/posts .