The polls in Iowa have really been bi-modal. And naturally, PPP sides with the colleges that have ridiculous Hillary leads.
32-41 point leads:
PPP
Monmouth University
Loras College
3-11 point leads:
CBS/YouGov
Quinnipiac
Des Moines Register/Bloomberg/Selzer (rated A+ by 538)
NBC/WSJ/Marist
Gravis Marketing/One America News
You left out the fact that the first three are also the most recent. All the others were conducted before Biden's announcement/the Benghazi hearing, and the last two were even from before the debate.
All of those polls didn't include Biden though, so it would mean that Clinton's lead increased by 20ish points (almost) solely due to the Benghazi hearing. That just seems odd given that the average caucus goer probably didn't even watch the hearing.
It was first after the Benghazi hearing of 11 hours slam dunk Michael Johnson basketball brilliance that everyone were saying that she had the general in the bag and that basically we could just call off the election altogether cause everyone already knew by 99% certainty how it would end. Yes, there's a before and after the debate and there's a before and after Biden, but ten times those two events combined, there's a before and after Benghazi.