Look at the Road&Track 01/2013 page for their comments regarding the ATS 2.0T vs ATS 3.6 and how "the V6 transformed the car" [their words]. They also mentionned that they "vastly prefer" this engine [again, their words]
Same feeling when I drove recently a 328i 2.0T and a 128i I6 2013. I have been driving the 128i for a few days and it feels in a totally different league than a N20, although it is a bit slower.
The 335i F30 fares better.