I have a 07 525i, and I just recently installed a rpi gt exhaust and sounds amazing, it's a little deeper sound and not at all obnoxious, I say start with this mod and you will love it check this website: Raceprecision.com and go to exhaust, call them and ask for eloy he designed these exhaust for our car model, he is a very cool guy and he will explain to you everything, and a gain of bout 7 to 10 hp with his exhaust.. Tell him Justin sent you and he will hook it up.. Hope i helped you and keep me posted.. Check out my thread on roof wrap and u will see some of the mods that I have done on the exterior...good luck!Just got a 2005 525 with 62000 miles wondering if there are any performance mods that can be made? Cold air intake? Exhaust? Has anyone ever done any of these to there 525?