Dear Ms. Silver,
In conducting some research on call center metrics I found that for the most part what you suggest as metrics are best practice. For example, both the city of San Antonio and the city of Chicago use call wait time as part of there metrics along with metrics such as call volume (see Links Below). However, I also found an audit done by the city of Sacramento that I think has some good information about how they thought about performance metrics and how to improve call center performance. I hope these resources help.
Research and Content Development Associate, ICMA