i run a minus 2 and love it. i dont ride flat track but when compared to my stock arm it really grabs and with the wheels right under your body, hang on because the front will shoot right up, lol.
i would highly recomend the minus 2.
as for the minus 3 i dont know never ran one but it seems alittle much. esp. if you have nerf bars because they will def. be rubbing the rear tires, but i would imagine you flat track guys just run pegs? so maybe it would work, like i said never ran a minus 3.
good luck and let us know what you get
peter