I see the numbers online vary from 300ish to 800ish at one time.
Is this very low, high or okayish?
RTS's I came from never had huge numbers in the first place (EaW, CCG, AoK etc.)
That's really low, even if it's just people in games / lobbies.
AoEIII usually had between 2k and 4k online at any given time unless it was late at night, when there were more like 1000-1500.
AoK was probably similar.
Warcraft 3 / Starcraft....thousands and thousands more than that (but they're in a different league of popularity, obviously).