i just have the straight though MP 4 blades and hit the 4 iron as well as i hit the 5 or 6 for that matter, 3 if i'm honest i don't use that much unless its windy.
But have have to say when i had some GI irons i struggled with the chunkieness of them and hit the blade so much better, but i have also worked on hitting long irons in the past, used to reg just take a half set with no woods and hiiting lots of shots in a real game situation rather than at a range helped a hell of a lot. i could in the future see the drop of the 3 but never the 4...and it wouldn't be to put an extra wedge in either