I don't think we should bench TM right now. However if TM continues to make poor decisions and show little or no improvement, I really think it's time to bench TM and start Brion as QB. Here's why:
1) Turner, Bell, and Enunwa are three young, outstanding wide receivers. I think Brion is a much better, more natural passer than TM. In the long run, I think Brion will be able to do a much better job of distributing the ball to these WR's than TM.
2) TM has shown little improvement. From what I can see, TM hasn't been making much improvement with regard to his decision-making. If he hasn't improved much by now, then he'll probably never improve much in this area. People -- including commentators -- sometimes say that he's young, but that's really not totally true. Had he not taken a red shirt, he would be a junior now, and he's had almost a full year of starting.
By starting Brion, obviously our running attack isn't as strong, but I think Brion is a reasonably good runner, and he is a much better scrambler than TM. What we gain in passing outweighs what we lose in running.
While Brion probably won't do better than TM at first, I think that he has a much higher ceiling.
Finally, TM doesn't have leadership qualities. I think he's improved in this area since last year, but he's still a relatively weak leader, on and off the field.