If you're talking about the 'racing spirit' and it's being called a "time attack" event, then shouldn't there at least be some effort to align with the original Rev Speed event rules? I think the rule of no slicks, any tyre up to semi slicks is my suggestion. Most competitors will not run street rubber if they want good times, so having a street tyre class, and a semi slick class is a silly thing. Just make it any tyre people want to run, but they must have tread pattern. Done. Remember, it's about keeping it simple.