[whpalmer4]

If you don't need to use the Duration/Estimate field, you could write an AppleScript that did a similar computation for each action in your database. But when push comes to shove, you've still got to make the same decision about which action to do next, and using this calculation makes for less transparency, not more...

If you do something like this, smaller numbers are higher priority than larger numbers, because the filtering and sorting assumes you want to find the actions you can do in a given amount of time.