I've been wondering the same thing.
Right now I am set up for long range as: 3W, 4H, and 6I... I've been choking down a bit on the 3W and 4H when I need to close the gap. It's not so bad from the fairway but I don't have much confidence shot making like this on long par 3's.
So, I've got the space to add 2 clubs and for the next round I'm planning to add the 5I (seem to hook the 4H when I try to swing easy) and I'm leaning towards adding the 4I too. I like the 4I when I want to keep it really low and when I'm striking the ball well. Feels redundant to keep the 4H, but I have a lot of confidence with it from the rough.
Anyone have a thought on whether I should drop the 4h in favor of say a 2h? I can't hit the 3W well from outside the fairway and wonder if the 2H might be as easy as the 4h? Plus I wouldn't have to choke down between a 3W and 4i.