"The Airbox" Maybe an exhaust system with 200 cell cats? Bilstein coilovers (I have them) and mods for faster shifting. That's really all I would do for performance upgrades.
2001 M3 Coupe TiAg/Black
PSS10 Coilovers | Turner Camber Plates | Lowe's Clutch Stop | Alcantara Shift/E-Brake Boot | BMW Performance Shift Knob | LED Tail Lights | Clear Front Reflectors | Headers with a Leak | Two New Rear Bumpers | 219M Wheels Coming Soon |