Which roller weights go best with technigas next-r?

I plan to purchase a technigas next r performance exhaust for my Kymco cobra cross 50. The pipe wont be coming with roller weights....so I am wondering what is the best weight to buy to maximize the scoot's perforance? How light should i go? (I weight 140 if that helps with anything). Thanks

Aprox. a gram lighter than the originals should do fine. +5 to the MJ and everything should be ok.