on my 3,0i engine I did get much better and deeper sound with X pipe than before and I was satisfied but I wanted to try make it even better and ordered muflers too. If i knew it will be too loud I would stick to X pipe. I am not sure about V8 but it should be deeper sound and I did not feel any loss of torque. Just give it try is not expensive and you can always take it off.
Let us know how it worked out for you

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My bimmers