I have the AFE Stg2 intake...got it for a good price. I would try and find one used to save some bucks. There is a few hp more than a panel filter, but mainly there is an improvement of intake growl over just a panel filter.
2013 M3 Coupe-MR/BLK ZCP, identical to my 2011.
2011 M3 Coupe-MR/Blk
2007 Porsche 997C2S Speed Yellow/Blk sport seats
2004 BMW M3 Imola/Blk