The OS F is actually hotter, but 'behaves' slightly colder in larger two-stroke engines.
I've found the OS F and Saito SS plugs to run slightly hotter than the OS 8 in engines that need hot plugs. There was some difference with those two 4 stroke plugs, but not as much as the OS A6.
The Tower plug is hotter. I now think it is cooler than the A6.