Recently I asked NGK if we need to use a cooler iridium plug when switching over from a standard spark plug.
They said, no - the heat range of a "7" standard plug is the same as the heat range of a "7" Iridium plug.
(ie: they've already taken into account the heat properties of both plugs - and while an iridium plug is 'hotter' than a standard plug - they've built both "7" plugs to be the same heat range - otherwise their cross reference charts would be ruining engines across the globe)
The heat range remains the same between the standard plug and Iridium plug so if you use a CR7HSA the iridium part number would be CR7HIX.
Rob MacDonald
Technical & Training Specialist
NGK Spark Plugs U.S.A. INC.
FYI- these are the proper NGK's for the LIKE 200i (CR7HSA, iridium/CR7HIX)
(DENSO: U22FSR-U, Iridium/IUF22)