The thing is, neither one of these guys (Grossman or Beck) are big play quarterbacks. It's not like Beck is gonna come in and go 20/27, 347 yards and 4 touchdowns. In neither case are we getting Aaron Rodgers or Tom Brady. It comes down to which quarterback will make the least mistakes, really. Is Grossman too much of a liability? He threw the four interceptions last week and, what?, two? the week before when we were leading.
Beck has that one drive and the fact that it's hard to be worse than zero touchdowns and four interceptions going for him. Grossman has the 3-2 record and the player's support (at least their public support) going for him. I really think you have to stick with Grossman and not make the switch until we're below .500 and fading. As long as we have a winning record, I think it would be a mistake to switch.
We're in a lot of trouble, though. Left guard Lichensteiger (or something similar to that name) is out for the year, left tackle Trent Williams is out for several weeks and tight end Chris Cooley is out indefinitely. Whoever is in there at quarterback is going to have a hell of a time on his blind side.