Stan, motors can change at any time, it's cells that are fixed from April to April. So Chris is right, when they release the motor in that combo, if nothing else is different (can, sticker, etc etc) I believe you can upgrade to sintered as by component they are the same motor.
I have run a 5.5 but with old cells and it was still freaking fast then. With new/good cells I can't really imagine ever using anything faster than a 6.5 but never say never
