The ring theory is interesting but I personally find it hard to believe it.
My problem is that I also see conflicting issues with the spinning top.
First of all it is my opinion that the top is a poor totem. If its sign is to spin forever in a dream, or fall over in the real world it seems too obvious and too easy for someone else to dream that behavior if they have seen Cobb use it or describe it. Arthur will not let someone touch his weighted dice, and Ariadne has a chess piece who's properties only she can tell - so no-one else can dream the behavior correctly. These seem like good totems. This makes me think that perhaps the top is not his totem and that as someone who trusts few people, perhaps the top is a decoy.
Contrary to this however, when Cobb is distressed by the dream he experiences in Mombasa, he wakes up goes into the washroom and spins the top and is interrupted by Saito. If the ring (or something else unknown to us) is his only or primary totem then to perform this display of spinning the top seems unnecessary as he thinks he is on his own - particularly as he seems hurried to try to use it.
If forced to choose between the top and the ring, I would reluctantly choose the top as his totem. Perhaps he knows something more about its physical properties that we have not seen.