Not bad for it is not nesessarily true.
I've linked the NGK numerous times on selecting plug gaps and heat range.
If the combustion temps are significantly increased, then you probably should go 1 step colder.
On a stock car, its not needed and I wouldn't suggest it. If a too cold plug is used, you could suffer from fouling the plugs at low speed or cold temps.
I'd really only suggest a colder plug on a fully bolted and tuned car where the increase in boost and/or timing will create hotter combustion temps, if your experiencing knock, or racing
2013 Ford Focus ST - Performance Blue, Cobb AP
Gone 2006 3 MPS Sports - True Red, Koni FSD shocks, in dash OEM look Ebay GPS/DVD, Hypertech, RX8 Rims