Well, without posting at amd yet, it seems some people have problems in general if they do all the GL init first (create context, create fb, create & attach textures/renderbuffers, then create the CL context) -- which is what this program does. It would mess up compartmentalization a bit, but may be worth trying before asking, to create GL context then create CL context then make GL buffers....
570/680 -- I've read so many discussions my head spins, mostly on the MacRumors board threads, so I'm probably confused. It's clear that the 680 is crippled in double-precision float performance, but hasn't become clear for me on single-precision. But it does kinda look like the 570 is the way to go with nVidia. Yes it is a pity that nV seem to be playing the pouty child with their CUDA vs "Open" CL.
I was very excited about the GCN cards, but don't know when Apple will provide support. The GTX 5xx/6xx seem to work out of the box with 10.7.5 drivers. But, if the interop works on the 5870, it should be enough to do 33ms frames at 1024x768, which would be fine for now.
(Far OT now, but that should be okay; the question has after all been answered and the thread is winding down with other info that may be of interest to a curious reader....)