How to transfer raw video data from a device to a computer using royalty free wired connection?
Anything much wrong with SDI? Or Ethernet? 

You are only looking for about 50Mb/s per screen, so simple Gb Ethernet will more then suffice, and even OLD school SD SDI could be leveraged as a physical layer with plenty of spare.

Hell, USB II would probably just about get her done, pain in the tail to implement compared to Ethernet however. 

Regards, Dan.