To MarkPek,
Relocate Masters is under the File menu. A window comes up which I can no longer see because all my masters are now on an external drive. If I remember it asks you to choose various options if you want to rename your masters. But if you just choose "Same Project Name" and "Same File Name" or something like that, it will keep the projects the same and the names of the pictures the same if you've named them.
I was just going to test it on one picture and only selected one picture but it put all the masters from all my pictures on the external drive and I couldn't cancel or stop it. Before I started I set up a folder on my external drive and that's where I chose as the location to move the masters.
According to Frank you can move them back with "Consolidate Masters" if you ever want them back.
I haven't actually worked with the library since but it did seem just a little slower than before when I clicked through a few pictures.