If you go the DENSO route, there are 2 types of iridium plugs.....the Long life, with the 7mm tip (which I recommend of the 2 types) and the Power Plus, with the 4mm tip
I recommend the Long Life 7mm tip because they are rated up to 120K miles.......the Power Plus with the 4mm tip are rated, by DENSO for 30K miles.
The Denso long life iridium has the platinum on the ground tab as well.
I don't know how Denso does in your particular vehicle....DENSO and NKG are highly respected brands......and it seems that NKG it getting some thumbs ups from other GM folks.