When it reaches 3.9, it usually mean that it is safe and that the fermentation is going well.
I don't think there is a specific pH at which it can start being called Activated EM.
You could drink it, but there will be a lot of sugars left, and a lot less antioxydants and other beneficial substances than desired. There might be the same number of total probiotic bacterias, I am not sure. The longer fermentation time will mean more phototrophic bacterias, and these seem to have the capacity to detox (by "digesting" many toxins). I'm very excited by that kind of stuff, it can be used to depollute our planet.
There's almost something spiritual with EM. They are said to be syntropic organisms, meaning that they create order, the opposite of entropic (disorder).