Today I picked up my 2015 +4 having had the Aero Racing exhaust system fitted from manifold to twin tailpipes and have done 80 motorway/country lane miles in it.
They also sent off the ECU to the factory to have the CS upgrade at the same time.
Dave has previously given an excellent expert technical review of his car having had the same done, so here is the abridged completely non technical layman's view:
It's faster down the range........a bit
It's faster further up the range......a lot
It pops and bangs.........alot (maybe too much)
It is loud and raspy on acceleration ..........alot
It tends to "hum" (is that the drone Dave was talking about?)........alot
On the whole, at this early stage, out of ten I would give it seven (nine if it was quieter).
I'm sure I'll get used to the noise, however, in the unlikely circumstance I decide I can't live with it, which is the noisy/hummy/droney bit that I replace to make it quieter (I asked to keep the old system)?
Manifold?
Cat?
Silencer?
Twin tailpipes?
Or is there another way to reduce the noise without replacing bits?
Thanks.
A volume control wouldn't go amiss, maybe I should have it converted to electric!
is on board to reduce the noise where possible (but sometimes I forget 
).