One of the Sun Ray engineers responded to my question regarding the new Advanced options. I realized what "Video Input Disable" was last night before reading his reply, but basically on some models of Sun Rays, there is a source button to switch to using the Sun Ray as a monitor for another device. In some cases, this is problematic (for instance, when using Sun Rays as kiosks, or in places where users are apt to press random buttons to get things to work). I wonder if the option would be more aptly named "Source Button Disable" instead, since initially I thought "video input" was referring to the composite video in port on Sun Ray 1 models.
The Fast Download apparently improves tftp firmware downloads over high latency connections. I've found that firmware downloads in the default mode over my home broadband connection are reasonable, though, so I don't have a strong reason to test this feature now.