Just to add my 2pence worth that might help out.
I'm APR stage 1 and had a Evoms fitted a day after the map and the car sounded great but couldn't really say it made a difference but the noise felt like it was. Anyway I started to get compressor surge had it Rolling road etc etc and spoke to a very clever guy that told me I was getting to much cold air, that's what's causing your surge sound between 2500 & 4000 rpm.
After a few days I though nah can't be right. Few more days passed with it playing on my mind, to much cold air I didn't want to believe it, so I took the Evoms off and put standard air box back on and bought a Pipper Cross panel filter. All I can say is wow, the difference is unbelievable.
No more surge, no more stupid boost leak sound, the revs pic up a lot faster and the car just feel and seems to run a whole lot better. And put a smile back on my face.
The very clever guy I spoke to tunes cars for Racing etc and fair play knew his stuff, and told ,me the only way you will benefit from a CAI is when you get to stage 2+ as the map, fueling etc all alter so the extra air is needed, but at stage one its not worth the money and also alters the performance.
I know some people might not agree but that just my view and my findings from having Evoms and then Pannel filter so thought it might help someone out.