we were getting 15 fps from 2 separate cameras at 640p on the odroid u3 in 2014 (were obviously not used much after the little FMS issue was found). I believe
the company that makes them has moved on to make cheaper and more powerful alternatives now.
You really can get a lot more out of doing vision processing when running it on an independent board. Not only can you get better framerates, but you can test your code without using the roborio, and with a proper monitor.