Dear Dave, just wanted to say thanks for this vast amount of information that you created, facilitated and maintained.
I fitted some parts to my Passat B8 wagon, I haven't come as far yet to fully evaluate the effects but it looks neat on the bottom.
Before I knew anything about this topic, I replaced the half aero tray with the kevlar 3Q0 alltrack skid plate. That was fun, removing front bumper...
After that I fitted the rear 5Q0501733 and 5Q0501734 lower wishbone aero covers at the rear, they work with the 4Motion rear axle.
Then I ran into this topic and saw some other options, out of curiosity.
So I ordered the front aero covers, albeit different part numbers since I have the 3Q0 front wishbones, so the part 3Q0 numbers are not relevant.
They did fit in combination with the 8V0 RS3 brake coolers though, that was interesting.
The full exhaust cover works with the 4Motion platform after fitting 5Q0804421B, just like you wrote.
I took the 5Q0825230H cover that does have a heat shield.
I'll try the Tiguan 3Q0199110B rear front-subframe cover as well, but I'm not sure it will work with the aluminium subframe.
It will be a nicer option than the 'double' Audi metal tray I think since I prefer the kevlar plate over a full metal plate, both in strength and acoustics.
I think this is probably the most I can get.
Since I know you want to keep this info focused on the Golf so I'll not elaborate on Passat specific parts.
But thanks for all the effort you did, really cool.