Why NGK Iridium? More Durability and a Higher Melting Point compared to Platinum, better center electrode anti-oxidation and anti-erosion, improved ignition, superior anti-fouling, lower required voltage, new metal shell plating process for better anti-corrosion. One Step Colder plugs are reccomended for cars with heavy modifications. These NGK plugs will get your Turbo Subaru running smoother and free up some power through increased efficiency and increased heat resistance.
I always go for NGK to keep my STI running at its best.