255/55R18 - 2.7 bar front, 3.1 bar back, I think. I followed VW's recommendation for heavy load found inside the driver's door.
If you are getting even tread wear across your tread at 3.1 bar it might be a good idea to put that in the front too. I personally like the tyres hard and make the suspension do more work, as long as tread wears evenly.
If the middle or the edges of the tread is wearing faster then the tyre isn't gripping properly.
Tyres sun a bit cooler with higher pressures too - within reason of course.
That's one reason why I stayed away from Goodyears for so long, they were always a soft tyre and more pressure didn't help. They seem to be better now.
I take more notice of what the tyre manufacturer recommends for tyre pressure rather than what the vehicle manufacturer says.
As for the question regarding viscous coupled center diff... No idea, unfortunately!
No, you don't have a VC centre diff.
I was having a go at noobytoogy and his attention to equal tread depth.
Mismatched tyre height is a problem for VC diffs; the uneven rotation speed between the input and output causes a massive heat buildup in the silicone fluid and it hardens the fluid.
When that happens the unit stops acting as a differential gear and locks up.