(I moved ya over to the N/A Performance Mod for the 900/9-3section)
Another thing you can do is remove your airbox, and increase the size of the intake tube with some PVC pipe.
Your stock intake tube (plastic paper towel roll sized thing) is fairly restrictive.
Purchase some 3" inner diameter pvc pipe from a hardware store or Home depo.
Cut to a length a bit longer than stock tube.
Cut larger hole in lower portion of airbox. You will remove the original tube and create a hole large enought to insert the pvc pipe.
slide new pvc back and forth inside box to size it so it will fit in stock location. then cut the extra protruding into airbox.
Glue, and Paint, and throw in a nice K&N panel filter.