People in Irmo's conference (Lexington, South Aiken, North Augusta) are tough.. Many games against great in-conference people. Like Region III-AAA with Riverside, etc.
Point is that anyone in that region (top teams) is going to have a great "opponent's %" because all of the teams are really good.
Might be interesting to see whose conference as a whole has the best out-of-conference winning %. That might take some time to figure out but would be interesting.
Agree with your IRMO %'s - they do play a tough schedule.