Answered my own questions by using this thing called the World Wide Web:
Since joining the conference in 2006-2007, UNC's biggest margin of defeat to a Big Sky opponent came last season, a 25 point loss--79-54--to Weber State in Ogden on January 3rd, 2013. The second biggest margin was 23, which has happened twice. Once to Idaho State 86-63 in Pocatello (in the very next game after Weber) on January 5th, 2013 and back to that inaugural season, an 89-66 defeat to Montana State in Bozeman on February 21st, 2007.
And yeah, tonight's 91-55, 36-point win IS the largest margin of victory for UNC since joining the conference against a Big Sky opponent. The previous high was 30, an 84-54 win over Sacramento State in Greeley on March 2nd, 2011. That was the last regular-season game of the year when UNC clinched the regular season crown and the right to host the Conference Tournament. The next highest total is 27, a 77-50 victory over Montana State here in Greeley on March 1st, 2009.
The more you know.