You might want to try the same shaft that’s in your 5 iron. You really don’t fit shafts like what you are suggesting. Wedges get fit, then irons are another “bucket” of clubs, then fairways, then driver. Each should be fit as stand alone groups of clubs. If you don’t like a steel shaft in the 4 iron and want graphite, try a heavier shaft, weight between the iron and fairway. Maybe something in the 90-100 gram range. You really need to try to get a fitting.