I'm a noob with spark plugs too.
What do you plugs look like when you take them out?
I have found some interesting reading at the NGK site this page in particular
http://www.ngk.com.a...k-plug-analysis
This page kinda backs up what The Mafia said about tune might be the problem over bad plugs, could it be a bit lean with 15 psi and standard injectors?
I was using 8's (which it had when it was imported) with similar mods you and about 250kw, but after about 4000 k's took them out and checked them, figured they might be a bit cold for day to day driving as they were black as when I took then out so guessed they might be fouling up and went back to 7's which have been in for 11,000k's without a problem so far.
As is said I am a noob, and would be more then happy to be corrected, so I can learn more about it.