The E53 (X5) bezels are completely different to the E39 one.
First of all if you try to use the 5 series one in the X5 it will be too small and there will be gaps all around the opening aperture.

The X5 bezel is rounded on the face of it and the 5 Series is flat so there will be a major looks issue there.

Look at the finish on the proper X5 (E53) install here:

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You cannot say that a 5 series is the same as an X5.