So which ones would be best to get for my a3 with I/H/ENGK plugs:
NGK-IZFR6K11 = stock A3
NGK-IFR7G-11KS = stock A2 (1 step colder A3)
NGK-BKR7EIX-11 = stock A2 (1 step colder A3)
NGK-BKR7EIX = stock A2 (1 step colder A3)
NGK-BKR8EIX = 1 step colder A2 (2 steps colder A3)
NGK-BKR9EIX = 2 steps colder A2 (3 steps colder A3)
Denso Plugs:
IK20 = stock A3
IK22 = stock A2 (1 step colder A3)
IK24 = 1 step colder A2 (2 steps colder A3)