I didn't guess he was an Epic, though I did think there was something more going on with the tensors at the point you mentioned -- maybe that the power was "all in the mind", that every human possessed the potential of an Epic and using the tensors allowed you, over time, to access the power without them.
I did pick up on Megan being an Epic, though (didn't realize she was Firefight, or even a double agent). Not immediately... but when she died, I immediately remembered the bit from the beginning about how some Epics could reincarnate and knew Brandon wouldn't keep her dead. Especially since her death seemed too perfectly tailored to drive home that she COULD NOT HAVE SURVIVED.