Agree with all above, and while there are no real conference strength rankings in D3, one thing you can look at is SOS (strength of schedule) rankings across a conference. For instance, in both the Massey’s and Boyd’s World 2013 season rankings, the 9 Northwest Conference teams occupy the top 9 SOS spots in all of D3 in Massey, and are nearly the same in Boyd’s. So, basically those schools all play very tough out-of-conference teams, and win a good percentage of those games.
So, you could look at a school like Willamette, for instance in the Northwest, who ended-up with basically a .500 season record, but beat Linfield, etc. and say they are a very tough team on a National scale.