The Paradigm Monitors are good starter speakers but there are better things out there now. Audioholics did a
round up of $800 bookshelves and your Elac U5 were on that list, so it's not surprising that you like them. Nothing wrong with going with Elacs all around if you like the sound, but there is tremendous value in the JBL 590 right now; $2000 worth of speakers for $800 is hard to beat. I have not heard the 590 but there are several members who have been very happy with their JBL Studios. Nice thing with JBL is that they make some good center speakers as well. If you can wait for a sale or will consider used, I would ask around the forum for a good matching center when you are ready. There are some options better than the 520C.
Paradigm also has the Premier 100B bookshelf in that price range if you like Paradigm's voicing of their speakers. The Premier center is also very good but the price will be higher.
If you go with the JBL 590, you could look on the used market for JBL surrounds to help save up for the center. There are some older JBL bookshelves that still sound very good and make nice surrounds, unless you're set on having the Studios all around.