It is the Bitcoiner at the exact opposite end of the scale that you need to concern yourself with. I read that only 3% of all Bitcoins are in regular circulation. The rest hoarded. About half of them owned by just 49 early adopter whales. These whales, whoever they are, will know very well that Bitcoin is hyperinflated on the back of limited supply being combined with the surge of interest from China, which is being brought to an abrupt halt. Even at $800, these guys know that Bitcoin is wildly overvalued. It will just take one of the these guys to get nervous or break ranks and make a grab for gold (Bitcoin is not gold, USD is gold) and this market will take exactly the same kind of slaughtering that any hyper ramped penny stock market takes when the early investors/ ramp masters decide to close their position.
i've heard this during every single consolidation period we've had since the climb from 2 back to 32 in 2011-12
there does come a point where those guys you speak of, the whales, will not need any more capital from bitcoin to necessitate the risk of selling out more than trivial amounts, where the risk of not being in bitcoin outweighs said selling
I wish there were statistics on the performance of those dumpers you speak of. I wonder how many were able to buy back more bitcoins than they sold