Heck I wish I could find it... there was a Pit Picture of one of the E3-diamond-fire whatever team's between round thrash from 2009 or 2010 that was circulating a while ago...
the mechanic/tech was gapping AUTOLITE spark plugs!! In the pits! with people watching...
I will be first to admit I have found the limits of my beloved FoMoCo plugs in my 5.0 builds... I've actually done some spark plug testing, on a chassis dyno. Drove the car to the dyno test, 60 mile drive plugs had 3-5,000 on them. cooled the car dyno'ed the car. Cooled the car, put in fresh FoMoCo plugs, same range/same part #. Ran the dyno test... picked up 3hp 2tq at the wheels with fresh plugs. That is what everyone claims with fancy plugs. then we cooled the car again, put in identical heat range NGK, regular copper "v-power" off the shelf plugs. No other changes, laid down another 7hp & 4ft, if memory serves me. Had I reached the limits of the FoMoCo design with all of my aftermarket iginition parts & the original "balance" was no more? Good arguement.
The car was one of my Mustang II's with an EFI 306cid, TFS aluminum heads, Cobra Cam & 1.7 rockers, Cobra intake, PMS piggy-back programming, MSD billet distributor, Taylor wires, MSD coil, etc etc etc... a very typical n/a SEFI small block. 350ish to the rear wheels through a 5 speed.
The old adage "the dyno doesn't lie" may or may not hold true.
I've witnessed in person tests on '04-up S/C Cobra's changing just OE plugs for Irridium, other platinum, & even E3's.... other than the A/F going all over the place, no real change... other than the initial fresh plug jump.
Rob
ps: mechanic, thanks for having my back on a typically defensive topic.