Obviously we're talking about backs in their prime and I'm not sure I've seen a better overall back than Adrian Peterson. He's got size, speed and tremendous power. The backs 20 plus years ago like Emmitt, Eric Dickerson and Earl Campbell didn't face the defenders with the size and speed we see in todays game. Peterson has shown in a passing league with no QB that he can carry a team on his back and although he has a good OL it's not The Great Wall of Dallas of the 90's. If you put a young Adrian Peterson even the Peterson of today behind the Cowboys OL he would rush for well over 2000 yards if he stayed healthy.