What is the advantage of an iridium plug over standard Stig, especially if they are the same heat range.
The simple answer is that they last longer. If you poke around a bit you'll find that's the one thing that folks agree on.
Of course that means the smoother idle etc. from a newer plug will last longer as well, but if you're the type who frequently replaces your plug anyway the main benefit will be to the manufacturer's bottom line.
There are some who'll say that it has a better spark, but actually it's very slightly the other way. Of course there's another myth regarding the spark strength there since once a spark plug has sparked, unless it's extremely weak, the fuel/air has ignited so that's that. With a fresh plug there is effectively no difference.
So...I run Iridium in my Burgman which is a true PITA to get at the plugs. I run copper in my Kymco since it doesn't get the miles that the burger does so the longevity of the plug is somewhat moot since it's about an extra two minutes to check, & gap or replace the copper when checking the valves.
I ain't gonna put up links to back this since I did my digging long ago (there are even youtube hits to back this if ya dig a little), but also cuz plugs are like religion. You're really not going to get many converts even with the extra efforts. If you're really interested poke around and you'll find it.
Cheers, & flame on.