I'd like to suggest that the default performance graphs be a little less rigid in what you can display. Currently you get a top ten, then next ten, or specific single volume to view graphically. I'd like to see the ability to select your own 2,3,4 or 5 volumes to display in the same graph. I know this can be done using the reports feature but that needs more initial work to get the view setup that you are after and it is sometimes necessary to select several volumes at once to see how they are performing in comparison.
This could then be used in other areas to have greater granularity into views without needing to create reports or export data manually first.