As someone who just turned in a 2009 335i with the N54 TT engine I can tell you there is nothing like having all that low end torque. Nothing even compares.
The new "ATS-V" definitely has to be equipped with a small-block V-8, or else the car should be re-named! The "V" should only be used to designate a "V-8"; if you're going to put a six in it, even a twin-turbo V-6, it should be called ATS-6 or even ATS-TT but not designated a "V".
IMHO the "V" should always, Always, ALWAYS be reserved for a classic "V-8". As with the original Cadillacs that sported a "V" and every GM car produced since, that "V" has a certain "cachet" which should not ever be compromised ..