John Terry thinks he is worth 4 or 5 wins. I think that is an exaggeration. But the two goals I project he might save may be worth an additional four points. If scored in the right games. Draws become wins.
So long as Arsenal play as well as they did in the second half of the season, during which they scored 42 points, then Cech's contribution puts them on 88 points (42x2 + 4). That's a title-winning total.