Ever drive a VQ with a manual trans?? They are rough as hell in the midrange to higher RPM's, the engine isn't balanced. Every review I've ever read of a 350/370Z G35/G37 has said the same thing. The vibrations make it seem like the motor is going to come apart.
I'm not impressed by Nissan's 3.7 because it has no advantages. It sounds like crap, has a narrow powerband, and its very rough. Plus it doesn't get any better fuel economy than an LS engine, despite the fact that its much smaller.
GM's new 3.6 DI is a very smooth engine, and it gets 30MPG highway. So it actually serves a purpose in the lineup.