A) The fact that graphite irons dampen feedback is a big reason why people use them at all. They dampen vibrations. I guess I could look it up, or you could go to your local Golfsmith, find unused graphite and steel shafts, and tap them on a table.
B) Not sure I can put a number on the fact that I lose the feeling of lighter-shafted clubs (which all graphite-shafter irons on the market are as far as I can tell). Happens with some lighter drivers too.
C) I guess graphite shafts don't have to be whippier, but all of the current iron models are exceedingly so.