It makes no sense whatsoever to start the fan before the stat is fully open - your are just cooling still water in the rad. Standard Caterham stat is 88deg, many people use an 82deg stat (me included) and the R500 stat is 74 deg.
On my Emerald controlled high power K, the fan is set to come on at around 96 or 98 (can't remember which) and off again at about 92 - this works fine (and is about what the normal fan switch is supposed to do). The fan should only really be required when you are stationary or moving very slowly - at any decent speed the airflow from the car moving will be much greater than the fan can produce. At the Longcross sprint on Saturday, waiting in the queue with the engine fully up to temperature, the fan cut in and out as necessary to keep the temperature in the low nineties on average - as soon as I started the run, the temperature very quickly dropped to 80ish.
I think people get a bit panicky about K series temperatures and try to overcool the engine - I am sure this is not the right thing to do as the engine needs to get the oil up to its correct operating temperature. Even in the heat of this weekend, my oil temperature never got over 80 deg, despite the water temps mentioned above.
Yellow SL #32