Leave the plug gap stock - the plug gap has more to do with ignition system performance - not plug tip heat.
Its like this - An ignition coil can only provide so much power.
The further the plug gap - the more power (KV) required to jump the gap.
The more power needed to jump the gap - the less power available to keep the spark arcing.
Wide plug gap = coil, wire, resistor cap dammage possible (may also run poorly and have poor mileage).
Normal plug gap = good ignition performance and enough spark voltage to completely (or close) burn all the air and fuel.
Close plug gap = spark plug burns longer than normal - but produces less heat at the spark - plugs foul.
Plug heat range has to do with the length and reach of the spark plug electrode.
The more of the electrode exposed to cylinder heat, the hotter the plug will run and the more heat retained in the cylinder.
A plug with an electrode encased in alot of ceramic disipates heat easier into the plug shell than a plug that has less ceramic around electrode.
A cold plug has less ceramic around base of electrode and disipates alot of heat to the plug casing - cylinder runs cooler
A normal (for lack of a better word) plug has an average amount of ceramic - some heat is disipated - cylinder runs normal
A hot plug has less ceramic at electrode base - a little heat is disipated to the plug shell - cylinder runs hotter