The main reason I did it was the sound. If you have ever seen a straight pipe turbo Diesel, on of the forst things that always catches my ear is the whine of the turbo. Just drive around a parking lot for awhile with your windows down and you will really hear it well.

That is also one of the main reasons I did the K&N. Going down the highway at full boost, you can REALLY hear the turbo sucking in all that air.

Both of these also free up two of the biggest restrictions in the system, and to me, reducing turbo lag quite a lot.