X-Pipes are a leap forward in technology, over the H-Pipe.   Due to the firing order, engines pulsate.   X-Pipes smooth out this "pulsation" to allow for a smooth balance between cylinder banks.   Translation:  Less back pressure, less heat build up, and better exhaust scavenging (scavenging is the ability to allow burnt exhaust gasses to exit the combustion chamber faster and more thoroughly).  The result is a significant increase in power and torque, as well as noise cancellation.   What more could you ask for?
 
Your X-Pipes should be mandrel bent (keeps its shape throughout the bends with no flow reduction-no kinks), 16 gauge aluminized steel or stainless steel, with or without catalytic converters, and off or on-road use, depending on your requirements.  X-Pipes with catalytic converters should be high flow.
 
Greyhound Performance offers several types of X-Pipes.   We have the GP 2 piece X-Pipes that are a custom made, tried and true product that we have been selling for many years.   All GP X-Pipes with cats use the MagnaFlow high flow converter.  We also highly recommend the MagnaFlow 1 piece, stainless steel Tru-X Pipe, with or without catalytic converters.   Also available are the MagnaFlow Tru-X crossovers sold in 2.25", 2.5" and 3", as well as their Y-Pipes.