Typhoon
For me, I played stiff steel for a number of years in my irons. As I got older and less athletic, couldn't generate nearly as much club head speed, I downgraded to a lighter steel shaft (about 3 years ago). I didn't see much difference in distance (the ultimate goal was to not lose distance overall), but did notice an increase in spin and more potential for variance in accuracy.
What I've learned since switching to lighter shafts - I need to keep my transition more smooth and not over-swing to get a good result, whereas I could swing all-out with a stiffer shaft and the ball would stay much more on line, simply because the thicker shaft naturally wasn't prone to allowing the face to twist at impact because of the higher torque properties.