Here's some information you just may find usefull -
An H pipe helps equalize the exhaust pressures between the two banks of tubing as the hot gases and sound waves travel down the tubing. This, in effect, relieves the exhaust pressures as they travel through the H tubing, generally creating an increase in torque. This will also give an added sound reduction when the sound waves combine inside the H tubing.
An X pipe will actually help to scavenge exhaust pulses from one bank as the opposite exhaust pulse passes through the X, thus creating a vacuum effect at the valve, resulting in a cleaner burn in the cylinder. This generally equals added torque and, like the H pipe, a reduction in sound as the sound waves combine in the X pipe.
The Y pipe, which works well on several applications, utilizes a dual exhaust off of the manifolds/ headers and runs back a specified distance, then the two pipes enter the Y pipe and become one larger pipe. This Y helps each bank to scavenge the other as the pulses travel down through the Y and are joined together into the single common tubing. This creates a vacuum in the exhaust valve, resulting in a cleaner burn in the cylinder. A sound reduction is also achieved as the sound waves combine in the Y pipe.
Personally, I've had both in the past and the biggest difference I've found between an H & X pipe is predominantly sound. As long as all things are equal, there's no significant difference in performance between the two.
Truck was sold today [5/19]. I got an offer I couldn't turn down. I had no more need for a pickup so I cut it loose. About to purchase a '14 Jeep SRT8 this week.