These types of questions are so subjective:
Do people get in with a 680? YES
Can you get in with a 680: YES
Does a higher score increase your chances: YES
I know you're looking for some concrete answers but your not going to get them. A 680 isn't terrible but it is about 20-30 points below the avg for most schools you listed. If you can take it again and do better maybe you should....
if not its time to roll the dice....
At least its the verbal that is the problem and not the math. If you english is great you can make up for a lot with well written essays and perhaps even addressing your low score in the optional essay.
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