Wow...this topic never dies....
Your midpipe is doing next to NOTHING to make power, so long as it isnt a bone stock crimp-bent-cated H pipe from the factory. As long as you've got something aftermarket, it's only going to differ as much as 5hp if anything, and you're NEVER going to see that kind of gain.
It's almost ricish, but just go with what sounds best to you. Most guys will swear buy an X pipe because they do in fact flow better than an H, but aside from that, the power gains are still minimal at best.
If you've ever seen a cross section of a Prochamber, it's a lot like a big wide and opened up X in a way....but will definately outflow both an X and an H, but does tend to quiet things down slightly, while adding a bit of a rippy sound at higher RPMs.
They're the best IMO.