Caribe Piranhas vs piranha natteri?

I currently have 4 piranha natteri and i was considering buying about 7 caribe piranhas to sort of liven up the bunch. from what i've red online they are suppse to be more active and aggressive when feeding than the nat's...but are they? since Ya is a forum i thought i'd ask REAL people who have no vested interest in me buying from their store or source for that matter. thanks