I say air-water does not cool as well because the water is always slightly above the ambient air temperature and heats up as it progresses through the core vs air-air that has a limitless supply of cool airflow over the entire surface.

I know the difference is small but its still there.

I agree, the actual installation of the turbo is more difficult than building a control system for the vanes. The vacuum/pressure control system works nearly perfect for me.

Another option thats been tried is the mechanical linkage although it looses some of the VNT's low RPM boost benefits in normal driving.