Simon,
You say the the better you get the airflow, the higher the temperature for a given speed but that sounds counter intuitive to me.
Are you sure the mods you've made have improved the airflow?
My thermostat is rated at 92 - 102 which means it starts to open at 92 but is not fully open until 102 so in theory my engine could also get up to 102 but because of the radiator capacity and the relative ambient temperature and engine load it seems to sit around 95.
That means that my thermostat is never fully open at normal operating conditions so some of the coolant flows through the rad but some still flows via the bypass circuit showing that the radiator has a surfeit of cooling capacity for my engine output and ambient temperature .
On a very cold day the thermostat hardly opens at all so the temperature sits nearer to the 92 lower limit.
I can only see one temperature sensor on the blacktop but you may have a second gauge or fan sensor in the water hose lines.
You can't avoid having a cooling fan in the system and I think it was just bad luck that the relay failed. It is highly unlikely that the engine will overheat on the move as the normal airflow cools the water in the rad. It's only when the airflow stops that the fan is needed. (If your system is working as it should)
Of course if your fan is constantly cutting in and out, the relay will fail sooner than normal so it is worth trying to understand what is happening.
One way to diagnose what is happening is to rewire the fan to run off a stand alone temperature sensor and see what temperature it switches on and off at.
