My buddy just got his single turbo converted FD tuned and was told instead of using 2 BUR7s and 2 BUR9s just to run 4 BUR9s. Is there a benefit to doing this with a mostly stock car or is this something that the higher HP cars with aftermarket injectors are doing?

 

Mazdatrix - Spark Plugs

 

Yes, 9's on a single turbo will be appropriate, even at near stock boost levels. I think NGK is the best choice but in my experience, the extra cost of platinum wasn't worth it.