itr cams will net you more power, but not necessary. it depends on your budget for everything. if you have extra money then get them. for the manifold, the performer x doesnt just "drop off", but the victor x is definitely more suited for top end power. where do you want your powerband to be? that will really determine which manifold to get. if you dont mind having less midrange and hella power up top, get the victor x. if you want some midrange and just continue up top, get the performer.