I've had a number of fittings specifically focussed on iron shafts.
My personal preference is majority stiffness towards the tip, with a heavier weight. I had x100's that i could not load correctly. On fitters recommendation, moved to a $taper 130x, which contrary to the above I feel is too heavy. I've got Modus 120x in my 48 & 54 wedges which work well. Testing a zxi7 with modus 105x in it was the opposite with them being too light, but preferable over the 130 $taper. As with any fitting i go into, I'm open to anything anyone suggests and have access to trying most shafts/head setups.
I should add that the current clubs with the 130x $taper are 620mb but are a lighter swing weight at D1. Willing to try any head, any shaft, any weight with preferences above. Thanks in advance!