From what Matt Watson said, the M3 is the trickier car to drive fast. So, can be argued maybe that the 911 base is just too clinical. M3 may give more thrills, especially to those who have professional driving skills.
I recall Deon Joubert's comments in January Car Magazine Performance Issue, when he tested the M3, he said that it was a better car for the skilled driver since you need to learn its ways and it will reward you.
I guess for most drives, the AWD M3 may be the real 911 Carrera 2 killer...