Don't mean to sound like a jerk, but why go nuts over why your end result is improved bro? There are so many factors that change so frequently...

• Not all plugs are created equal, even the same exact model #
• Not all wear states are created equal, and it always changes
• Not all engines are exactly identical
• Weather changes hourly
• Fuel is not guaranteed to be 100% consistent batch to batch in the same brand
• Break-in and startup methods
• Heat saturation states
• Clutch setups
• ...to name a few

All of this stuff is just theory and practice. Even a scientific mechanical engineer couldn't get you a 100% infallible answer bro. Too many things change when looking for the answer (but he'd probably be a killer pit guy when he was done...lol). I completely agree though: this IS counter-intuitive. Why? Who knows... and enjoy your cooler temps, better bottom, more top, and longer runtimes. Woot! Woot!

As a tuner I can say that a cooler plug gives you a wider tuning window. Perhaps you were at the rich edge of that window and only experiencing 80% of that engine's potential. When you found the sweet spot in the narrow hotter window you are now experiencing the engine's FULL potential.

Great job tuning by the way!