Just a fly in the ointment on the benefit theory ,when I had my C109 Boulevard (twin plug heads)I took the plugs out for a fiddle and to check the colour for combustion performance , and found one of the plugs had no sign of an centre electrode, we looked at it through a high power magnifier they use to check diesel injector nozzles (a black art) and it looked like it had never had been there since new ,thinking AH! here comes a performance improvement with a new set of Plugs ,guess what not one bit of difference it ran exactly the same , it was running just fine for 8000k with one dead plug ,and just fine but no different with new plugs