Seems fine eyeballing it, but let's double-check.

Using "Profile GPU Rendering", it seems scrolling the tabs makes no noticeable difference with LWTs enabled, but adding or removing tabs sees a slight momentary decrease in performance when the tab is initially added or removed. Both themed and unthemed, this spike takes longer than a full frame to render. Since this has such a minor impact, at least on my N7, I think there's nothing to be done here, though we may wish to optimize some of the animations down the road, with and without themes, if it's possible. WORKSFORMEYO.