Yes, I do like to keep things conservative, so you have to take what I say with a grain of salt. I'm way down south, so I have 100*F ambient temps to contend with too and there's lots of humidity which just makes everything worse.

If going fast is what you want, you might also want to consider a 7XL. I know that many who run in cooler climates have no problems running the hot motor. I have two of them and they do get a truck moving.