To verify the HW is okay, I installed the catalyst drivers (14.3) and am able
to run the same set of tests with no corruption at about 85fps vs 30fps with
corruption or 6fps without corruption.

The r7 260x is a fairly new card.  That it works at all with the opensource
driver stack is GREAT.  As demonstrated by the fglrx drivers, there is lots of
room for improvements though <GRIN>.