When the defense is snowballing the opponent and there's no pressure on him to carry the team, he's usually pretty good. It's those games where we get behind early and it looks like he's going to have to do something (see Cards, Niners this season) that he seems to go into his shell. There was some weird stat about how he had almost all of his 4th qtr comebacks in his first season. I don't remember the exact numbers, but it's pretty wild.
Anyways, I've had moments in the past where I started to believe in him, but after that absolute collapse in a game with a niners team that he had circled on his calendar after performing terribly and getting bounced the past 2 seasons from the playoffs against, I'm out completely on him and the only thing changing my mind is him playing great throughout the postseason and taking us to an NFCCG or SB.
Otherwise, he's not worth the extension he's seeking, and it's time to move on. Even his staunchest supporter agrees with that.