Personally, I would run the B6HS in the summer & the B5HS in the winter. A #7 plug might
work well for hard riding on those 120 degree days though.
The theory behind choosing the right plug is having a plug that is just hot enough so that it can burn off any gas or oil that sticks to it without being so hot that it causes preignition in the cylinder, (igniting the fuel/air charge before
the spark does.)
On the other side of the coin, if the plug's too cold it will foul out with gas & oil.
I hope this helps.