It should be pointed out that the club most often used as a measure for clubhead speed is the Driver. All other clubs will measure lower than the driver. It should also be noted that 99.9% of all players now use graphite in the driver, regardless of how hard they swing. The percentage is almost that high for fairway metalwoods too.
Where the preference issue comes in is with the irons. More players still use steel in irons, in part because of the real fact that you don't get as much feedback from graphite. Graphite shafts absorb more of the impact shock, so it's harder to tell when you've mis-hit and just how you mis-hit the ball. The issue of accuracy is no longer bourne out by actual statistics with the modern graphite materials, but most players haven't been convinced yet. If they were only for weaker swings, they wouldn't even make them in stiff flexes. My King Cobra irons are stiff flex graphite. But mostly, graphite just feels so much different that it's harder to make adjustments because it's harder to tell what's going on with the ball.
As your first responder said, you will most often find graphite irons in the bags of senior players and women because a weaker swing can see a real gain in distance with the additional flex or whippiness. The club will load more on a slower downswing than a stiffer steel shaft, then release that energy at impact if the player's timing is right.
The only clubs in my bag with steel shafts now are my sand wedge and my putter. My other irons are all stiff graphite. My 3 hybrids and my 3 wood are regular flex graphite. My driver clubhead speed is right at 95 mph, and I use a regular flex graphite in my driver. But I'm an old fart too.... 60 years young.
