I think you are referring to the heat and noise insulating glass which is something like double glazing and is a thicker glass that stops the heat and noise.
The privacy glass is the tint on the windows that is darker from the rear doors back and I would think would have a minimal impact on sound if any.
I've never had the heat / noise insulating glass so can't comment on that I'm afraid.
I have the equivalent of heat insulation glass on my ML, it does make a difference. Here is how I know:
I drove to work the ML (with heat insulation glass) and my 335d (without) on two consecutive days with about same temperatures in mid to high 90s. After about 9 hours of sitting in the sun, the ML was bearable and was able to simply get in and drive while the 335d was unbearable where I had to lower the windows and get the AC on max. Note, both cars are white.
Having said that, since I don't plan to drive my Porsche to work

, I did not get this option.