Just changed mine went with NGK Iridium LTR6IX, heat range 6. Really didn't need to the car has 21k on it. I have to pull them back out, gapped em according to the owners manual which is .049-.053. NGK recommends .044, what a dumbass.
Called a tech at Ford Performance he said they come pre-gapped, but the proper gap for my application is what the manual calls for .049-.053
i did mine at 83855miles not because i wanted to i just knew that previous owner didn't do much in the line of maintenance on the car and it was serviced at the dealership,i got the ngk rutheniumgapped to .052 and heat range 6 mfg recommended..car is naturally aspirated accept for the cold air intake cast was a little more that iridium but the amount i drive it i'll never need to changed plugs again in my lifetime. car seems to drive a little better but still has that split second lag from start i thought that the programmer would fix it but i was wrong..