Hard to compare this kind of thing, but subjectively the UI feels snappier with the under-the-hood changes, even basic things like opening and closing contents pane, the library menu, there's no longer any 'lag'.
Couple of UI bugs:
- in the book info pane, the 'done' button doesn't always appear immediately, pops up after up to 10 seconds.
- The link-set indicator is being overlaid by the book icon rather than the other way around.
In the library panel:
- The carat to indicate sorting floats to the right, and can disappear off the side of the panel.
- Clicking the menu above the book icons sorts by title and seems redundant.
- The default width for the rank menu isn't wide enough for a search with lots of results - the numbers clip.
Finally I couldn't really work out what the new rank menu was doing, is it ordering by relevance to the search criteria? If that's the case should that be the default?
Some screenshots:

