.055 is correct. The TR55IX and TR6IX that I mentioned are iridiums. On newer wbodys iridium is factory installed.
The one this I noticed when doing research on the Brisk is that the quad recommended for a stock GTP also has a foot note about potential blow out. Eventhough they recommend their iridium plugs for higher boosted application, it's not clear what configuration you get, Single, double or triple prong. I am interested in the soon coming review.
autolite 606 is stock, 605 is one step colder 104 is 2 steps colder and 103 is 3 steps colder than stock.