Everyone will have a difference in opinion and what is "overperforming" for one might be "basic or under" for another.

Mine is simple and to the point.

1. Under performing - no job stone, missing skills, no mitigation, not using abilities you do have, 10+ levels discrepancy on gear.

2. As expected - just that. You do what needs to be done. Not done perfectly but you know your role.

3. Over performing - i personally don't see it as "overperforming" as much as "going above and beyond". I typically like to stay in this zone. This means even if the content is easy...you focus up and do your job the best you can. Now doesn't mean I won't have fun with it. Hell I've died typing just making jokes as we go about it. All part of the fun. However other than that...A-Game all the way.