All X pipes
are inherently the same except the double helix. Mishimoto did a detailed test when developing their pipe and they found that the degree or config of the single x didn't have an affect on the sound or the hp. So if you get an X from one company it should be roughly the same sounding as any other and make the same difference in power (almost 0).
The double X should sound different since it has the gasses crossing streams twice instead of once but, I don't have any proof. I suggest you spend more time looking at the install vids of the system you are interested in or maybe visit different forums and post this same question. This forum is nice but it is not S550 intensive.
2016 GT Vert, SB, AT, 3:55s Weathertech, JLT, Steeda, Colgan, Velossa Tech, Coyote Spacers, Diode Dynamics, Shelby GT350 SW, Curt, Goodridge, aFe, MRT, BMR, Kooks, Mishimoto