I think Poehling is mostly whatever, he's a solid depth guy who fills that Riley Sheahan type of "4C eating defensive minutes" role pretty well. I'd never want to pay him any sort of substantial money, but he's really nice on a cheap deal in a depth role.
Petry's an absolute gamechanger on the 2nd pair, though. The combination of him behind Letang with a health Zucker and Malkin has completely revived the Penguins 2nd line. The Zucker-Malkin-Rust line is one of the top lines analytically this year, and I think having such a dynamic player in Petry behind them (like how the Crosby line gets Letang) has helped with that. The offensive impact from the blueline with having one of Letang or Petry on the ice for 3/4 of a game can't be understated.