ill put in my $.02. For stock bikes, T-6s, For ported, strokers, big bores, etc. T-5s. i built a stroker with T-6 and the guy wants me to (once i get my shee, hopefully this weekend ) get T-5s and trade him. i calling bull shit on the trade b/c im going to buy the same stroker kit and then i can do a test to see which runs better.