The F8DC4 run best in lean burn SFI engine
If you are stuck on NGK, go put them in .. but buy the Bosch F8DC4 at the same time so you will have them in hand a few miles down the road as I tried to explain to you..
There are tons of plug post in the archieves that witness the far superior running of F8DC4 on HFM/SFI benz engines ..and to the point that FastLane does not even bother with giving any other choice...as these have proven to suit BEST.
But,...From you NGK persistance , I think that our attempts to help you will not change this and that you have no choice to staisfy yourself but to buy-them, try -them, change-them..
Been there...done that..Good Luck..