There are some benefits to going a hard pipe kit. Worst problem is the cost. Check out the link below of guys modifying the existing twin turbo pipe to get the same effect as the trust/greddy suction kit. It can help with surge issues from bigger turbos. Also mspeed, hks, trust/greddy dont't fit them for the sake of it.
http://www.skylinesaustralia.com/forums/Tw...20#entry5406370