They posted the big upset PWR rankings on Twitter:
-Holy Cross (21) over UMN (2) in 2006
-Bemidji State (37) over Notre Dame (2) in 2009
-RIT (25) over Denver (2) in 2010
-RIT (38) over Minnesota State (1) in 2015
-Ferris State (30) over SCSU (2) in 2016
-Air Force (27) over SCSU (1) in 2018
-AIC (31) over SCSU (1) in 2019
Holy Cross was actually the highest ranked PWR team from the upsets, but it was the first of the #4 seed over #1 seed upsets, so it was huge at the time.
Going strictly by PWR, the RIT over Mankato in 2015 was the "biggest upset".
RIT has twice been the winner in these upsets...and SCSU has been the loser three times (every time as the #1 or #2 overall seed)...ouch.