You can try to run r600_demo, but you will have to add your pci ID in r600_demo.c - it's easy to spot where. I assume an RS780 is closest to an RV610 or so. Technically, it comes after an RV635, but it probably doesn't have vertex caches, like an RV610.
Currently there is no list for r600_demo, there probably will never be one. Best chances are on dri-devel, or on the radeonhd list.