This topic has probably been done to death ages ago.
I am currently using NGK DPR8EIX-9s (iridium's) in my 95 M900.
I run Kelley coils (have run Dynas) and Igniteck ignition.
I have also run the DPR8EA-9s. I have found the Iridium plugs and strong aftermarket coils stand up the higher octane fuels we run down under. I run the 98 RON/94ish MON fuel to stop pinging with JE hi comp pistons.
I read in the Igniteck thread that Chris Kelley found a 1-3hp increase with non resistor type D8EA plugs. I have no reason to doubt his claim based on my record of dealing with him. It appears that these plugs may be causing failures in Igniteck units so I have played it safe with the resistor plugs. If I could find a way around it I would swap to the better (and cheaper) plugs in an instant.
The projected nose plugs look better as they appear to give the spark more exposure to the air/fuel mixture. The D8EAs look like old clunkers in comparison, but looks are deceiving.
Now 1-3 hp in an 80hp bike is a significant improvement for ten bucks. Cheap ponies indeed.
I am running the Iridium plugs because I have found them to resist fouling with the dense higher octane fuels I run, but so far the dyno (over the last couple of years) has shown no overall hp gain with my bike . I do feel the bike is a little smoother and tractable down low but that is all.
So what is the corporate wisdom of the Forum on this?
I pretty much dismiss anyone who claims a 1-3 hp increase from anything.
You realize that can just be variance from one dyno run to the other right?
Besides, when it comes to spark plugs, unless you already have a problem (bad wires, fouled plugs or incorrect gap) then you shouldn't honestly see a difference with one good, properly gapped plug to another.
Personally I think too much time is wasted on plugs for bikes like this.
Now, if you're running a 600 hp race engine, then MAYBE it's worth the effort to consider the plugs more and maybe even index em.
But 100 hp or less bikes - nah.
JMHO - YMMV
The only relevant difference I've found in spark plugs over the years in many vehicles and applications is that copper is going to give you a SLIGHTLY stronger spark, and iridium lasts for friggin ever.
So, if you want a marginal, negligible, and utterly unmeasurable increase in power, go with old tech cheap copper plugs and change them every other year of average use.
If you want to change your plugs once every eight years but pay a premium for the convenience, go with iridium.
I don't have any scientific data to back stuff up, so just guessing/seat-of-pants experience. In my TLS I noted no difference between running Brisk plugs, *EIX plus and *EK plugs. The Brisk plugs seem like they'll last forever, the EIX plugs also last pretty well. The EK's are good for about 12k miles of my use.
I very much doubt that non-resistor plugs will improve performance. They may also screw up the bike's computer and inputs from various sensors. It's a totally different machine, but my trials bike goes totally wonky on non-resistor plugs. The trials bike certainly has a lot less electronics than any modern street bike, though they are all packed in a tight little area.
I've been told that resistor plugs produce a somewhat less intense spark over a longer duration while non-resistor plugs produce a somewhat more intense spark for a shorter amount of time. Six of one half a dozen of another as best I can tell.
In the end, I think once you light the fire you've done all you can and no gain is to be had from sparking more.
Thanks for all your candid responses guys.