ok, just got off the phone with ngk and learned some valuble info about which plugs to use. their rule of thumb is to drop one heat range per 100hp added to the car. for some this puts you into a really cold plug, which might produce some fouling at idle or city driving conditions.
we came to the conclusion that the stock plugs will work good in the stock-400whp range. for the 400-500rwhp range the LFR6AIX (iridium) will be the best choice. now for 500-600rwhp LFR7AIX stk.#2309 is the best choice. these come out of the box with a 0.030 gap, i would go about 0.030-34. now for 600-700rwhp it changes, cause the standard iridiums stop at 7 heat range. then you get into their racing series plug, yet still iridium R7437-8 stk#4901. the racing series plugs go all the way to heat range 10 for people taking it to the extreme.
the stock plug is LFR5AIX-11, so you can see the number that designates the heat range. also found out that over seas manufactured spark plugs use a different range for heat than domestic. overseas, the higher the number the colder the plug, domestic manufacturers are the opposite, meaning a higher number is for a hotter plug. don't get those mixed up when you go spark plug shopping!! lol

 

i will give a "plug" for www.sparkplugs.com also. i called around town for the LFR7A plugs and nobody had them in stock yet still wanted $15 each for them. i checked spark plugs.com, they have 100 instock @$7.06 each. well, now they have 94, hahhaa.