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I bought the double-irridium plugs from Rock Auto, SKP brand out of China.
All I can say is that the 2010 Toyota then passed smog prior to my selling it, and that the plugs were only around $4.50 each as I recall.
I've pulled plugs from a Ford Expedition 5.4L which is a difficult extraction, so better plugs make sense in terms of their service interval.
Plugs either spark or they don't, and the main variables are temperature, voltage rise (as realized at the electrodes), compression pressure, and plug gap.
Setting the plug gaps on the narrow end of spec (or narrower) not only allows them to go on sparking for a longer service interval, but also extends the life of the secondary windings in the coils.
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