You are misinformed. 217k BTC is only a fraction of the monthly volume traded on some of the largest exchanges: they trade 3-6 million BTC per month (http://bitcoinity.org/markets/list?currency=ALL&span=30d), so one could trade 217k spread over 30 days without causing swings. (Only if you did the trade at once, it would cause one sudden swing.)
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No, it would cause a pretty big swing. Large sums like this are unlikely to be put on an exchange, though - they'd be done through a private sale.
You are misinformed. 217k BTC is only a fraction of the monthly volume traded on some of the largest exchanges: they trade 3-6 million BTC per month (http://bitcoinity.org/markets/list?currency=ALL&span=30d), so one could trade 217k spread over 30 days without causing swings. (Only if you did the trade at once, it would cause one sudden swing.)
Dumping it all at once is what I had in mind.