Have you considered going quad tip? A lot of the guys have done that with great results (me included see:
http://f10.5post.com/forums/showthread.php?t=685790).
__________________
2011 535i xDrive, Dark Graphite Metallic, Veneto Beige Dakota Leather, Technology Package, M Sport Package, Executive Package delivered Christmas Eve '10, Mods - quad tips, 20% tint, JB4.