Funny how you mention it dying after 4000 RPM... I had the same issue when I just had the cat-back and it drove me nuts.
Like everyone said, if you wait a while you'll find some decent x-pipes without paying too much (mine were crazy cheap!)
2011 E92 M3, Alpine White, Black Interior, Carbon Leather Trim, Black ZCP Wheels ...DCT, ZCP, ZCV, ZP2
Mods: ZCP Spoiler, ZCP Mirror Caps, Black Hood Vents, Black Grills, Black Side Grills, Black ///M Emblem, Macht Schnell Spacers, RPi Catless X-Pipe, Gintani Sport Exhaust