We've run into this issue with a couple clients where users in course A with a small number of students view the assignment grading table and set their user preference to 'All' and then go to course B with say 2000 assignments, view the grading table which then times out.

There will always be some functional limit given the server setup, eg in this particular clients setup somewhere around 800 assignments on one page is where it times out or explodes, but practically a limit of around 100-200 is better and returns in a couple seconds. Our simple solution is an optional site wide setting maxperpage. If this was set then the 'All' option in the dropdown would no longer be available to be chosen, and any page size options which are larger than the limit would also be removed, and additionally at runtime the perpage would be capped at maxperpage.