Even with high quality fonts, 2000 is a lot for Font Book to handle. Personally, I wouldn't consider having more than 500 in its database. While no help for any font manager, Font Book is particularly susceptible to bad fonts. Bad fonts will mangle its database, and then its a fair amount of work to fix it (mostly in the form of figuring out which fonts are no good).
If you need to handle lots of fonts on a regular basis, I would suggest either Suitcase Fusion 4, or FontExplorer X Pro. If you do go with either of these, you also need to get Font Book and its database off your drive. Any time there is more than one font manager on your system, they will fight each other for control.