During the Solaris Desktop Summit we've determined that one of the
reasons for the new GTK L&F not performing as well as the default
Ocean L&F (up to 40% slower in our tests on SwingMark) is that the image
type for the images used for caching the widgets is always translucent.

We've found that some themes don't use translucent pixels when rendering
their components. ClearLooks theme is one example - most of the components
are either opaque or 1-bit transparent. Both of these types of images
can be accelerated by Java2D on X11.

Even in the Blueprint theme some of the widgets are rendered as
opaque/1-bit transparent.

With a simple hack to GTKCachingPainter.java's createImage to always
return INT_RGB instead of ARGB (so this is the "best we can get" estimate)
we got about 7% improvement in SwingMark score in the local display case,
and about 4x (yes, that's 400%) improvement in remote case.
(The local case shows even better improvement if text AA is disabled)

See some suggestions about how to implement this fix in the comments section.