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.