Here's how the long pause happened:
Data are on local drives on hub in USB 2.0 port. Library is somewhere around 150,000 tracks, most tracks are on the same drive. I took the ones I wished to remove from the library permanently, changed the name of their base folder (L:\Music to L:\retired), and after that operation was done, chose via that folder in a Disk Location view scheme, and deleted from Media Library only. Current track ends about 7 or 8 minutes later I guess. MC17 takes 30 minutes to adjust the library, after which the paused song scrobbles, and then the next song starts. The only reason I know it had not crashed was because I opened the task manager and saw J River using about 50% of my memory (4GB).
I'm doing a similar operation with a smaller amount of tracks to retire (about 1000) right now, and I'm going to just simply move the folder first, perform an import and let it remove the broken links. Hopefully this will not pause it.
The first way I'd tried it is more intuitive to my mind and the way I'd do it with little thought. The second way strikes me as "going around my thumb."
My large library is constantly in a state of morphing like this. I do so wish there were a simple menu choice that would bring up a cleaning dialogue (a la Ctrl-Shift-Delete in a browser bringing up the cache cleaning dialogue) that I could check off which "hidden items" in the library I'd like to delete from the library -- removed, CD info, network drives, and so on.. Because my library morphs so much I constantly have to keep it clean and barebones else I start getting ridiculous lag time for simple operations.