I'm going to do a H-pipe on mine. I already bought the SS tubes, SS mig wire etc, it's just the time that is missing.

A straight pipe is loud, but is not a nice sound since the exhaust pulses of each cylinder banks of the V8 are separated the whole lenght. It's a bit like having 2X a 4 cylinder engine... sort of. A friend of mine had a 1983 modified Toyota 4X4 with a high power Chevy small block in it, and he had straight pipes. It was loud but not like a muscle car, it had a higher note, but not like a M3. Hard to explain, but I didn't like it.

A member here said he lost some torque using a X-pipe (but gained some HP at higher revs), and since he is (like me) using his X5 for towing, he decided to remove the X-pipe and install a H-pipe. He regained all of the torque, and the sound was great.
Since the H-pipe connects both left-right tubes, the sound is like a V8. Mustangs do use H-pipes from factory and they sound great (to my ears at least.)

From what I read on some Mustang forums, a X-pipe will give more HP to the expense of torque, and the sound will have a higher pitch tone, more raspier. The H-pipe will keep the torque and no HP gain, and the sound will be more of a low frequency.
I know that most people go with a X-pipe, but I like to do things differently

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