Some more information regarding the newer OEM NGK sparkplugs from a forum member on Golfmkv.com:
When comparing to a bosch stock plug many goof on the difference in how their ranges work. Because of that some cross references out there show the 6 heat range NGKs being stock. If you go to NGK themselves and check THEIR application guides it shows a heat range 7 as being stock.
It seems that the newer spark plugs may not be one step colder. I wonder why they changed over from the Bosch plugs?
Here is the older article: New OEM plugs