The new Burner XD irons have a 17-4 stainless body and a titanium face. The face is supposed to be very thin and have a higher COR than normal irons and they incorporate their inverted cone technology (supposed to be the factor that makes their drivers have a high COR across the entire face).

Taylor Made also said their r7 irons were supposed to have a thin stainless face with inverted cone technology. I think I remember reading a claim of a 7 yard gain in a 5-iron shot. I doubt that was ever proven.

In a Frank Thomas article, the COR of fairway woods was explained. Long story short, he made the point that since a fairway wood face wasn't nearly as large as a driver face, the COR of a driver could virtually never be reached in a fairway wood. He explained that the trampoline effect that enhances COR is a function of the area of the club face. I think COR in irons would be a similar story as fairway woods. He said COR was not a large factor in fairway wood distance.

I wonder if I could find that article. It's probably around a year old or so. Maybe someone has their Golf Digest mags stacked up from recent history.