Personally I would look at the Milltek Cat-Back System for a bit of extra noise, and would be nice when topped off with a tune!
Here is a link to this system in Australia. Can also get in ceramic black exhaust tips.
http://www.evolve-technik.com/collec...aust-f20-m135i
And a comprehensive youtube test video of this system. (Ignore title, the uploader states it is a cat-back system only in the comments)
And link to our local tune as well. (235kw to 282kw, 450nm to 576nm!!)
http://www.evolve-technik.com/collec...-box-f20-m135i
I don't think a cat-back exhaust system will have any warranty implications (other then BMW not covering any faults with the new exhaust system); especially if retaining the OEM downpipe and cat. But the tune most likely would.
But once I take delivery of the M135i and add some decent km's, I might add the cat-back exhaust system and tune... I had these plates for the A45, but will now go on the M135i...
It will want the extra power boost!
