I'd like to say I have no limit but that's simply not true. With most of dramas, I really think that the ~20 episodes is enough. Often more than enough...
But then, with sitcoms I could keep going on for a long time. I've said this before, but High Kick 1 (167 ep) could've had hundreds of episodes more and I'd totally watch it. Also, I used to watch this non-Asian soap opera for about 2000 episodes, so uh, if there was an Asian equivalent... it wouldn't be the episode count that would scare me away.