The risk/reward and cost/benefit ratios don't really support it.  More chance of misfires, shorter interval between plug replacements or re-gapping.  For a gain that might not even actually exist.

I just replaced my plugs and I had one of "Y" plugs with five of the standard electrode plugs.  The Y plug was dirtier and more fouled.  Just an odd aide...

 

I went through the whole "push it to the limit" thing with plug gaps and timing advance and other stuff and finally realized that I couldn't tell the difference between the extra 5 degrees of advance or the extra .005" of gap, or whatever else I was messing with.  Dialed it all back and it's a lot less worry and performance is just as good.

On ‎5‎-‎1‎-‎2017 at 8:01 AM, Chickenman said:

 

I'd stick with the NGK 6 range if the engine is running clean. If it's pig rich and burning oil. then yes, 5's might be needed.

Just use BP6ES, I don't see R plugs necessary it's not a modern car. Heck I even use B6ES ( cheapest ones ) on my 240Z and they do the job just fine.

Going hotter is not the solution to existing engine problems..  if the plug is fooling it's either oil, or to much fuel, or in extreme cases the head gasket is leaking and fooling the plug.