The only design aspect of the 4 I like over the 6 is the headlights. The 6 has ugly headlights. Other than that the 6 is much more beautiful.
2013 ///M5 Individual
Monte Carlo Blue, Platinum Full Individual Merino, Platinum Alcantara, Piano Black, Exec Pkg, Drivers assistance pkg, Bang and Olufsen, 20" wheels
Eisenmann Sport Exhaust, Bel STiR+, Laser Interceptor QUAD HP, Zaon MRX