I have an '03 Dinan 4.6is with all the treatments minus the supercharger. It's rated at 370hp, up 30 from stock. It was a $12k upgrade installed at the dealer when new - before my ownership. I haven't driven a regular 4.6is or 4.4i for that matter but my engine revs freely, the power delivery is effortless and it sounds like a 700hp racebred engine. I often get compliments on the sound. I'm sure all parts are needed to get the 30hp and that price seems extreme but Dinan charges more because they cover the factory BMW warranty that's voided when they make all the changes, which shows their engineering and quality commitment. I don't know any other company that does that. If you're looking for sound, I would probably just do one of the popular exhaust systems but that won't do anything for performance (Dinan included). If you a want performance vehicle, it's best to start with a performance vehicle - 4.8is. Best of luck on the journey!