David Carr's signing with the 49ers could spell the end for Shaun Hill in San Francisco.

The move would not go over well in the locker room, but neither would the fallout affect wins and losses -- unless Carr got into games, at which points all bets should be off.

The numbers tell only part of the story for Carr, Hill and incumbent 49ers starter Alex Smith.

Hill has a 10-6 starting record and an 87.3 rating, but he was only 3-3 with a 79.6 rating last season. Carr had an 82.1 rating in his last full season as an NFL starter, completing 68.3 percent of his passes with 11 touchdowns and 12 interceptions. Citing that 10-6 record will become convenient if Carr gets into games and the 49ers fail to win. But Hill was clearly trending downward in the 49ers' offense, which was changing in ways that did not suit him.

Carr's career numbers, though poor for a player drafted first overall, aren't off-the-charts bad.

It's just that Hill seemed to possess some of the intangible qualities that make quarterbacks effective leaders. Carr and Smith haven't shown they possess those qualities in sufficient quantities. Those qualities alone aren't enough to make a quarterback successful. Not having them, however, can make it tough for a talented quarterback to succeed.

Would the 49ers be dramatically worse off with Carr in the No. 2 role and Hill elsewhere or in a third-string role? We could make that case based on the won-lost record, but that might be a little misleading.