I run NGK plugs in all my vehicles. Will be switching the G6 over in about three years, or when I get about 70,000kms on it, currently it just rolled over the 40,000km mark! I don't drive much to warrant longer lasting plugs. Not worth the money. I had too many problems in the past trying to pull a plug out of a head that's been in there for close to 100K kms. I can only imagine the trouble I'd have pulling them out at their rated 100K mile mark. I change copper core out every 40,000kms, never had a problem in twelve years, which is more than I can say for longer lasting, more expensive plugs.
If I drove 100K kms a year, I'd think twice and get the longer lasting plugs for less downtime, but as I don't, it's not beneficial to me to keep plugs in a head for 6+ years at a time, or longer as you're just asking for problems.