Understanding How the Default Resolution Preference Works

  • Hi folks,
    I am looking for clarification on how video output resolution works in Isadora 2\. My video files are currently 1920x1080 and running very smoothly at this size. However I need to use a long VGA cable run, 100 or 150 feet/30 or 45 metres, and so I need to output a smaller pixel resolution (say 960x540) to avoid signal degradation over the long cable run.
    My question: Do I need to re-output my video files from my video editing software to the smaller pixel dimensions, or can I use my 1920x1080 files in Isadora and set my Isadora default resolution preference to scale the video to the smaller dimensions? 
    And, assuming that I can rely on Isadora preferences settings alone without resizing my files, and that Isadora will be sending out a true 960x540 video signal from my computer - does the ongoing file interpolation add substantially to CPU load?