I've searched for this extensively but did not come up with anyone comparing the interiors specifically.

If, for example, you were to take a 2018 911 and a 2018 718 with similarly spec'd leather, the interiors seem very similar. Is that true? Is the 911 nicer interior wise in any areas when spec'd the same?

 

Same materials, same layout, just slight different in number of gauges, air vents, dash style. I've been in both and honestly don't feel any different when in one or the other. It's basically the same interior.

 

Interior has many Porsche parts bin...well parts. Quality is identical on the interior level between the vehicles.
The 992 and 718 is where you get the difference.