I think the N54 is a great engine too and turbocharged it develops stonking power and performance.
But, there are those of us who like a nice, linear, power curve, where power increases right up to the point where you hit the rev limiter. In the turbo cars (new M4 being a prime example), the maximum BHP is available from about 5,500rpm up to about 7,000 (or whatever it's redline is). That's not a characteristic I like. Where is that reward for holding on to the limiter, that you get in the Z4M's? That last 1,000 rpm gives you that extra kick. It's habit-forming. They just love to be revved and it's a natural, gorgeous sound. I don't like piped engine noises through the speakers either. All of which unfortunately means no new BMW for me next time around.