I've got the NGK Iridiums in now and don't notice a bit of difference. Probably last longer but I tend to change plugs before necessary like most of us.
Most I've read is indexing is a waste of time for the tiny potential gain.

 

There is a very well kept secret that if a guy runs a cooler plug in the rear cylinder and indexes the front plug with the bend of the electrode pointing at the center of the chamber and index the rear plug 180 degrees opposite you will pick up 10% tq at all rpm's. It only works with the Quadruple Unobtainium Flame Thrower spark plugs though and they are hard to come by.

 

Currently running NGK DCPR8EIX Iridiums. Has anyone tried the NGK DCPR9EIX Iridiums ? They are a heat range cooler than the 8EIX.

 

HD plugs are made by Champion at the Champion factory near Byesville, Ohio. My sister-in-law sent me a set when they started making them there like five years ago or so.

 

If you're speaking of the bike in your profile, V Rod, the "8" is the stock equivalent plug, right? The "7" is the cross for a big twin.
I run 1 step colder in my Ultra but not sure there is any advantage. You could try 1 step colder but I doubt you'll notice any difference.

 

NGK Iridium for me,

Plenty of Utube videos out there showing modest hp gains with a plug change only

http://www.cyclesolutionsonline.com/...park_Plugs.htm

 

My apologies. Yes I have a V-Rod but I also have a 2010 Ultra Limited. I was speaking of the Ultra. Yes, the "7" is the direct replacement for the OEM plug. I'm running the "8" now and have not noticed anything.

-Tim

 

A couple builders have suggested that a step colder is good for builds with higher compression. 10+. As I mentioned earlier I have one step colder on a stock build (stage 1) now and don't think they have any affect good or bad.