the temperature of the plug has nothing to do with the external temperature

what its got to do with is the ability to absorb heat from the engine
a colder plug will (if ive got this right) absorb more heat, meaning it will not pre-detonate as easy
thats why the scoupe turbo plugs are a range colder then normal, as peak pressures and temperatures in the cylinder are greater then in the standard alpha engine
the standard plugs in the scoupe turbo wont be able to get the heat away quick enough and will start to pre-detonate
well, thats my understanding of it anyway - it could be totally wrong