As far as best wins you would have to go all of the way back to 2015 to find a comparable win when we beat Nebraska. Before that all of the way to 2014 against Texas.
Before that we played very few top "P5" teams on the road to even have a chance to win. But some games that easily trump Tennessee were Oklahoma (it was a road game with 80,000 opposing fans even if it was dubbed neutral), TCU and Utah.
The point though is you would have to go back pre-Mendenhall to find a team as low ranked as this team at BYU...except for the fact we have the past 2 years as well. Consecutively we have the 3 worst BYU teams from a ratings standpoint since 2003. But yay we beat Tennessee!