I've done a bunch of benchmarks on the new beta driver and xrender, and render_bench is the only benchmark that shows these great results without any tweaking. Specifically, setting InitialPixmapPlacement to 2, at least on my 8800 gts.
A better benchmark of xrender, that shows results closer to what you would get from real applications, is expedite. And yes, evas software rendering is still almost twice as fast as xrender in the overall expedite results.
Soooo... if Qt is compiled with XRender support then KDE should be more responsive in 2D, right? What about Gtk and Gnome?
From what i've seen, the only way to get these results is to set InitialPixmapPlacement to 2, which has the side effect of slowing down almost all gtk apps by a very significant amount. I'm not sure about qt apps, but I would guess it's the same.