for which car bro?one step colder helps the car to reduce knocking due to our hot environment,the oem for my corollas 2nzfe are denso ik16 but im using ik20 from the day i bought the car,reason being same that i explained above.
ive got both ik20 n ik16,u can use ik16 if u want,ik20 was a personal suggestion 