The 380 is a bit of a waste of time in my opinion. I looked into it FULLY. Was very very close to selling the BMW and putting the money towards a 380, BUT the way they make the power is a complete cludge and they've had to cut off 500rpm to make it work reliably. Which in the real world means it actually doesn't really make any more usable power. It's a bit of a con to be honest. There are quite a few 380 owners who are learning this recently. A few of them VERY unhappy about it, especially the track focused guys...
Honestly, unless you're planning to track it a lot more than use it on the road, trust me, the 345 bhp is PLENTY!!!
As for the noise, I presume you're talking about the titanium option exhaust? It sounds absolutely superb but my GOD it's expensive. Scarily so. Prohibitively so. You could have one made that sounds just as good and is more track friendly for a mere fraction of the cost. Like less than a quarter! And you get to spec the tailpipe design you want...