In an upcoming Rhino WIP OpenCL support is much improved. Assuming OpenCL compiles for your AMD GPU it should run with comparable speed to CUDA, albeit slightly slower. Responsiveness should be in the same ballpark as CUDA.
OpenCL rendering is still not the main focus for our integration effort though, partly because OpenCL rendering in Cycles isn’t entirely feature complete yet. Transparency might not work properly in all cases, and HDR textures (float textures) for environments are converted to byte textures, since without that such textures come out entirely garbled resulting in funky lighting and even weirder environment renderings.
Anyway, I hope that OpenCL rendering works on more devices now. If it doesn’t there is one thing you may want to try as AMD GPU user:
Add to your environment variables two new variables:
If you have old variables that point to the split kernel you should remove that. After changing these variables make sure you restart Rhino.
If that still fails please report.
Thanks and have fun.