Ok, I'm sensing not a lot of love for the idea of McGrath as a medium pacer. I know others have put his name forward, but I initially included him so I'll seek to explain my reasoning.
a) I agree if anything he's more 'medium-fast', not 'medium'. (although sometimes still 'fast-medium')
b) He has got slower from what I've seen, and I've not seen much of him since the Ashes, where for most of the time he had an injury he was recovering from. He seemed to be consistently bowling in the 120s. That is not fast-medium - its almost Steve Waugh pace and nobody called him fast-medium.
c) I think he bowls in the style that I've read about great medium pacers bowling, rather than your classic fast bowler, ie emphasis on accuracy, variations of movement, and speed, rather than intimidation (with the ball, the face and mouth are a separate issue), and pace.
d) I'm sure I've seen Gilchrist keeping up at the stumps to him on a few occasions in either a 20/20 or ODI. That he hasn't done so in tests yet is probably because McGrath would kill him than because it wouldn't be doable when McGrath is bowling at a slower speed.
e) None of this detracts from McGrath's bowling at all. He obviously still delivers the ball with enough on it to make it very difficult to play. In his heart he'll always be a menacing pace-man, much like Tiger O'Reilly liked to feel like he was the reincarnation of Spoffoth in attitude etc.
All that said, I wouldn't disagree with anyone leaving him out of their calculations for the reasons people have offered previously.