If you are talking about catted AR downpipes then it give you 10-15 bhp which you hardly notice. You will feel turbo's spools a little longer but not much difference since you are running sports cat not the catless version.
MY08 E92 335i M Sport|Wrap by Surrey Project |ETS Intercooler|VSRF Dp's|BMS OCC|BMC filter|CoBB AP|EBC Yellow & Coolcarbons rear|Alpina AT Map|Michelin PSS |CF grills,CF mirror,CF Performace spoiler|LCI light|CIC controller retrofit|2014 Mods: Birds B3 Suspension kit,Project Mu pads,Afe Filter and PTF Protune & Pilot sports cups. Gone:Forged FMIC, Eisenmann Race Quad, Eisenmann Sport Dual, Duke Dynamic Diffuser. Eibach Pro springs.