I suggest searching and listening to some sound clips (here and youtube). It will help you decide for yourself.

While straight pipes are more aggressive, I think you will be happier using the X-pipe. The x-pipe doesn't have as much cracking/popping so its smoother sounding.

Here's my 04 4.8 but its not the best representaion. The engine was cold and the audio function on the camera was crappy.

2004 BMW 4.8is X5 only with X-pipe - YouTube