I have a site with the same issue. It has over 800 pages. I have read elsewhere that WP has issues with lots of pages (not posts). Has something to do with rewriting of the permalink structure.
I'm on a machine with a ridiculous amount of memory and processors, so hardware is not the issue. It only effects the modification of a page (whether it be in Quick Edit, moving to trash, or normal edit mode).
If I try to perform any of those actions in bulk (more than maybe 4 pages) I would end up with a blank white screen. I just recently extended the PHP memory to 200 from 64 and the timeout to 180s and now the processes do complete without the white screen, but it takes many 10's of minutes for things to happen. Does anyone have any ideas?
P.S. I've also run WP-DBManager's db optimize and repair to no improvement.