I will talk out of experience that the E46 M3 has a great engine and handling control but you don't really want the SMG II.
Also, the convertible is a little bit less stiff and will have a bit more rolll because it's eavier than the coupe. In order to gain most performance you need to keep the needle over 5k rpm when the rasp sound kicks in. Get the stock 18" wheels they are less easy to curb and the 19" optional ones look like plastic toy wheels. The manual 6 is perfect for a sportscar like this.
A must have upgrade is an eisenmann meistersaft exhaust...
www.eisenhaus.com
