I think having a no esc limit is good. Just stick with the fdr at being 4.2 or slower depending on track. I run a spx on profile 8, I like the speed. At our club track we have about 10-12 every week. We will continue to run the old rules just because everyone likes the speed. Since october when we started racing carpet, I have finally worn out my tires after racing every weekend and haven't broke anything since July when I ran asphalt.