You guys do know that "hot" or "cold" on a spark plug is just a matter of the insulator shape and it's join to the metal body, right? A "cold" plug transmits more acquired combustion chamber heat to the cylinder head. A "hot" spark plug has more exposed insulator (acquires more heat) and less ceramic insulator material connected to the metal body so it sheds less acquired heat into the head and stays hotter.
A spark plug has to be "hot" enough to resist fouling at low engine temperatures and speeds. It also has to be "cold" enough to avoid detonation at high engine temp/speed. Higher-performance engines, generating hotter combustion-chamber temps, need a colder spark plug to keep the plug tip within the ideal operating range.
Now that I'm thinking about it, I wonder if my bike (143cc BBK and V2 race head) could benefit from a plug colder than stock.