How to create a performance template with goals's overqualification?

Summary

the client needs to measure a goal when is exceeded on the requirements.

Content

let's say that we have a sales group where the manager set a goal of 20 pair of shoes sold in a month, the client wants to measure those scenarios where a worker sold more than 20 pair of shoes in a month, for a reward on those extra sales.

¿there's a rating model that can handle this type of scenarios?