Just for the heck of it, I went back through Smith's stats for every game for the past 2 years that he started. 25 games regular season, and 2 post season.
In the regular season, Smith threw for a total of 30 TD's and 10 INT's. There were 11 games out of the 25 where Smith threw more than 30 times. In 10 of those games he threw for 11 TD's and 4 INT's... which is roughly right at the same ratio. In the other game... against the G-men... he threw 0 TD's and 3 INT's which skews makes for 11 TD's and 7 INT's which skews the overall ratio.
On his biggest stage of his career at the time... playoff game against the Saints... he was taking on Drew Brees who had thrown for just under 5500 yards, was completing 71% of his passes, and had thrown for 46 TD's. The game got into a shootout in the 4th quarter, and Smith answered Brees not only once, but twice with the game on the line. 42 passes for Smith. 3 TD's and 0 INT's. And the win.
The next week, on his now biggest stage of his career... playoff game against the Giants... he had his team in position to win by leading a TD drive late in the 3rd quarter to take a 14-10 lead. Then the first of the two turnovers on the punts. The Giants take the lead 17-10 midway through the 4th. Smith responds by leading the 49ers to a 1st and 10 at the Giants 15. A 5 yard pass has them at 2nd and 5 on the 10 with 6 minutes plus to go in the game.
Now at this point, Smith threw an incompletion on 2nd down, and completed a short pass for 3 yards to set up a 4th and 2. The 49ers kicked the FG to tie the game at 17.
Did Smith shit his pants on 2nd and 3rd down? Were the play calls conservative to make sure the 49ers were tied at worst? Did the Giants defense just rise to the occasion?
I really can't comment without seeing the plays.
But bottom line is this. It appears Smith can throw the ball 35 times a game and still take care of the ball. Outside of 1 game, his TD/INT ratio is the same. And his 5 TD - 0 INT performance in the playoffs indicate the stage may not be too big for him to handle.