Hi-COR irons, high tech yadda yadda irons are designed for those over 75 mph mid-iron. It's why single length hasn't caught on with the senior lessor club head speed crowd IMO. Our mid-iron club head speed isn't designed for 4 deg. loft gaps it's more 5 deg to 6 deg.
mid iron speed over 72 mph – 4* increments (average player)
mid iron speed 60-72 – 5* increments (some seniors and some ladies)
mid iron speed under 60mph – 6* increments (seniors and ladies)