Calling all Reporting experts! Is this possible?

[SamanthaIsin]

Hey all, here's my ask. I need a report that...

1. Displays the name of all my proof approvers who have made a decision in the last 3 months
2. Sorted by...
3. The average amount of time it takes for them to make a decision from the proof creation date.

I'm about halfway there (I think). I have a proof approval report with all the approvers who have made a decision in the last 3 months. I also have a calculated column that gives me the difference between the proof creation date and the decision date. It's aggregated to give me an average and when the report is grouped by approver I can easily see the average amount of time it took each approver to make their decision in the last 3 months.

Here's the problems I'm facing -

1. I can't sort by an aggregation. Thus, have no way to order the names by the time it took them to approve and don't believe I can create a calculated custom form field that would easily tie to proof approvals and make it sortable.
2. The report is massive. I'm getting over 9,000 results and when you sort by approver name and THEN apply the approver grouping then the line items will collect by users. Otherwise they're scattered and I'll get 104 line items for Billy on one page of the report and 130 line items for Billy on the next page. Aka bad data.

Is what I'm trying to do even possible by some magic without exporting what I have into Excel and manipulating it there?

This report is a direct request from our VP of Global Marketing so the pressure is on! Help!

[SamanthaIsin]

Partial solve. On problem number 2 I can avoid the issues related to the report being massive by only viewing the summary page which is a culmination of every result. So now - how do I get an aggregate of a custom calculated column to display on my details page?