I think if both teams are healthy, the Sox are the better team; however, while both teams have the injury bug now, the Sox have been hit harder with it throughout the entire season. There's little doubt in my mind that if Papi hadn't missed a month and a half, the Sox would have the best record in baseball. And that's not even taking into account Lowell's injuries, Manny tanking it, and the short DL trips of Dice-K and Wakefield.
So in my mind, a lot of this comes down to how healthy the Sox can be over the next month+. If Drew, Lowell, and Wake all come back in the next week or two and Beckett's numbness is just a minor issue, I think the Sox can overtake the Rays.
Think of it this way too: would you think a 4.5 game lead was enough for a team to clinch the division at the All Star Break in the NBA? Because that's essentially what we have here with the Sox having 36 games left, just a shade under 1/4 of the entire season.