+8 here. Avon 200 rear tire.
im at +3 over running 18 lbs. and dont lift or spin with my Hook-up. I do have an AMS tho. im just wanting something a little longer for the track but dont want to sacrifice my street manners too much. stock shock revalved. I have an undertail and its faily low and not even close to rubbing.
I was +6 but now i am back to stock length and love it