The N20 is a great engine with plenty of power, I have it on an X1. If you feel like you'd like more power you can get a $400 tune from Burger Motor Sports. I ordered the M235 but if the convertible had been available I would gave gone 228 M Sport. Not everyone that buys a BMW has to have a track car or race at each stop light. It will be plenty fast so don't sweat the decision.
1995 325i, 1996 328ci, 1997 528i, 1997 Z3 2.8,2001 X5 3.0, 2001 330i Convertible, 2002 M3 Convertible, 2003 M3 Coupe, 2004 M3 Coupe, 2004 Z4 3.0, 2004 X3 3.0,
2007 X3 3.0, 2007 335i Convertible, 2013 X1 28 sdrive,
2014 M235 manual