Just on your other comment about scroll performance. I don't notice it significantly slower between the two styles, it has always been very stuttery and sluggish to drag the slider with the mouse in calibre regardless of which you use. I don't know whether it is because of lots of "stuff" calibre is computing underneath for each row or a Qt issue where it is trying to figure out what to paint on screen.
Scrolling with the mouse wheel is usually far less sluggish - in general usage I try to filter down the results using searches/keyboard shorcuts and avoid having to scroll
