Oh that sucks. I didn't know there was a problem with the 08 STis And not covered by warranty really blows. Is that when you went with your current Legcey?
Why go a step colder on your plugs? A colder plug can reduce problems with in the engine. Reduced heat is good for summertime...
Here check this out... http://www.ngk.com/glossaryImage.asp?imgID=94 I also posted a pic to click on.