I've installed NGK (5464) BKR5EIX-11 Iridium Spark Plugs.

But becasue I'm Hong Kong, should I use a cooler BKR6EIX instead?

Your esteemed advice is really appreciated.

 

Heat range of spark plugs is not related to outside air temps. The OEM plug heat range has proven to be just right.

 

I think you're golden...NGK irridium's are what came from the manufacturer

 

Iridiums are definitely the way to go. I use them in all my "modern" engines. I don't know about heat range options, but as far as manufacturers go, I put a set of Autolites in the XKR a couple of thousand miles ago (found them at less than $2 per plug) and she's running great. I put a set of Champions in a Northstar engine 4 years ago and they're working out fine too. I like NGKs (they were the only plugs that worked well in my BMW 635), but as long as you use Iridiums, I don't think the manufacturer makes much difference.

 

I used the Bosch platinum's and they seem to be fine.

 

Several years ago I tried the Bosch Quad Platinums once and thought they ran terribly. I heard the same from other commenters at the time as well. I think the single and double Platinums were OK though, but for my money I only use the Iridiums now.