I use HKS SuperFire Racing Iridium plugs (s40i, heat rating 8), Keep in mind that I am running the 1JZ-GTE twin turbo at a high boost level (1.2bar/17.5psi), well high boost for the stock turbos.... So they would be overkill for the sc300/400 n/a
But if you are going turbo or already are then these would be a very wise (somewhat expensive) choice.