I adjusted the capture portion of the OpenROV software on github to use video 4 lan and native MJPEG performance in place of the OpenCV code. OpenCV can still be easily tied in after translation to YUV or RGB conversion if desired.
The performance is much better with 15 fps performance at 640/480 with minimal lag. This is tested using 10/half-duplex T but not with twisted wire.
Here is a shot from 'top' looking at process and memory usage:
Code attached below: