In case anyone actually checks this thread, I was advised to run a larger than stock gap on my iridiums to increase resistance and be closer in that regard to the stock coppers. I'm going to go ahead and do that.
???? I've never heard of that? NOT saying its wrong, just saying with all the myths floating around about ignition and spark plugs, I suspect that it is just another one of those myths, but I don't know. And the fact a lot of newer motors have problems with different brands/types of plugs, which no one has explained the reason why to my satisfaction, it just adds to the confustion.
Increasing the gap will increase resistance, that is true.
What I don't know is true:
Is if Platinum and Iridium plugs have any different resistance than Copper plugs. The more exotic metals are used because they last longer under the stress of carrying an electric arc over the surface NOT because they have a lower resistance.
I don't know if minor differences in resistance has any real effect on the ignition system as well. If it did, you would think that the spark plug wires being different length would throw off ignition systems, yet most motor have spark plug wires of different lengths and the wires have far more resistance per foot than the plugs themselves.
I don't think the plug gap is determined by the manufacturer by resistance, I'm guessing it is more likely experimentally derived while testing the engine design according to all sorts of other variables, the least of which would be resistance, but I do NOT know that for a fact.
Finally, the plug gap recommendation from the manufacturer has some practicallitity to it. The gap will increase as the plug wears out, so the recommendation usually means the smallest gap that works well, so that as the plug wears the performance doesn't suffer. So, your increased gap may still be well in the range of good performance for the motor, but since its closer to the "too big" of a gap, it means you'll suffer poor performance sooner as the gap grows. BUT, that is just speculation on my part.