I used the 21 degree 585 H to replace my 3 iron, so I would say the 24 degree would replace your 4 iron.

Not to be smarta**, but the one that you hit the desired distance.

I doubt either will replace a 4 iron if they have a graphite shaft.

Yes, the 24* is approx the same loft, but with a lighter longer more snap graphite shaft you will hit it longer.

Possibly if you get the same shaft that is in your irons you may get the correct distance.

Its been my experience that a hybrid with loft of 5iron and a graphite shaft goes between 4iron and 3 iron, but I have a 503h 22* with steel shaft that goes about the same as my 3 iron, I just like my 3iron better.