If your goal is a 'better' sound by way of an X pipe, it won't matter which X pipe you choose, assuming the diameters are the same. As far as longevity, it might matter how it is built and the thickness of the tube walls.

If you want or also want to improve performance, "theoretically", the X pipe will increase scavenging. The greatest benefit of scavenging is a lower RPMs. As the RPMs increase scavenging decreases. I think the scavenging benefit will be minimal. Greater scavenging is not always good.

I think the best route to improve the sound and gain performance would be to remove or replace the resonators or mufflers with less back pressure versions. Less back pressure is always good.

There is the potential, no matter what you choose to do, that the change will create a drone in the cabin. Over time or when driving a longer distance the drone can be very annoying. To be sure that didn't happen I would do something someone else has already done so I would know what my X would sound like and if there was any resulting drone.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas