There is no single magic temperature for egg poaching.
At the risk of oversimplification: it won't work because the proteins in egg whites coagulate at a higher temperature than those in the yolks. A poached egg works because the white temporarily protects the yolk. It coagulates first, and once it's firmed up, the task is done. If you leave the egg in the water, the yolk will coagulate, and you're well on your way to a hard-cooked egg.
Now, if you could control the temperature instantaneously, bringing the water temp down from about 80°C (white coagulation temperature, more or less) to 60°C (five degrees less than yolk coagulation temperature, more or less) the second the whites have set, you might have a workable system.
ETA: as has been pointed out elsewhere, a poached egg is not a sous-vide egg.
