Hi antartican,
First off, a 680 is a great Score - and depending on your Quant and Verbal Scaled Scores, it could be enough to get you into your first-choice School. As such, a retest might not be necessary. In an earlier post, you named some highly-competitive Schools, so you would likely find it beneficial to speak with an Admissions Expert about your overall profile and plans. There's a Forum full of those Experts here:
https://gmatclub.com/forum/ask-admissio ... tants-124/If you do choose to retest, then it would help to define this recent performance in more detail. To that end, you might choose to purchase the Enhanced Score Report. While the ESR doesn’t provide a lot of information, there are usually a few data points that we can use to define what went wrong on Test Day (and what you should work on to score higher). If you purchase the ESR, then I'll be happy to analyze it for you.
GMAT assassins aren't born, they're made,
Rich