Demon,
Why do you think you may need a colder plug? When you have the correct heat range, do you know what the lower & higher temp limits are for for reliable spark delivery?
I can think of a couple of reasons to go hotter, not colder.
I don't think I necessarily need a colder plug but, if I want to add some spark, it should not hurt it either.
I worked for an OEM on engines my whole life. Always target to get the coldest plug that doesn't foul under the worst conditions, be it granny starts and drives or repeated cold starts at -20F. High cyl pressure (i.e. high power) engines use colder plugs (colder than production) for high speed/high load extended durability tests. You want to prevent any type of hot spot in the chamber - spark plug or otherwise.
Drag racing isn't exactly an extended test but it is certainly a high speed/high load test.
