Should I sell (and buy back more later) or hold??
Hold...
I say sell some and buy back. Reason being I believe this is temporary pump then back to 4000. It would be silly not to when we are seeing 20% swings in 5 minute gaps. Just don't gamble your main stash but use clear cut chances to increase your stash!
If we were all to adopt a strategy like this its more likely to weed out the pumper dumpers long term by taking their coins.