Here are some other QBs numbers for this season only, it's tough to find compiled career splits.
Drew Brees, when playing from behind, has an 85.4 QB rating. He has thrown 9 TDs, and 10 INTs. In the 4th quarter, with the game within 7 points, he has a 72.2 rating, and has thrown 4 TDs and 6 INTs.
Kurt Warner fares a little better. When playing from behind, he has an 89.8 QB rating, has thrown 13 TDs and 8 INTs. In the 4th quarter within +/-7 category, he has an 85.6 rating, 6 TDs and 5 INTs.
Eli Manning, when playing from behind, has an 78.8 QB rating. He has thrown 4 TDs, and 3 INTs. In the 4th quarter, with the game within 7 points, he has a 115.4 rating, and has thrown 4 TDs and 1 INTs.
Eli Manning, when playing from behind, has an 83.2 QB rating. He has thrown 11 TDs, and 7 INTs. In the 4th quarter, with the game within 7 points, he has a 80.6 rating, and has thrown 5 TDs and 3 INTs.
Brett Favre, when playing from behind, has an 80.3 QB rating. He has thrown 6 TDs, and 5 INTs. In the 4th quarter, with the game within 7 points, he has a 82.5rating, and has thrown 4 TDs and 3 INTs.
Tony Romo, when playing from behind, has an 107.9 QB rating. He has thrown 9 TDs, and 3 INTs. In the 4th quarter, with the game within 7 points, he has a 146.4 rating, and has thrown 5 TDs and 0 INTs.
Now you tell me based on those results who you would want QBing your team with the game on the line, or attempting to lead a comeback.
Tony Romo, without a doubt.