A viable workaround for HD video, and OpenShot, is to first transcode to HDV (high definition MPEG-2) or to high quality MJPEG using for example the command line "ffmpeg -qmin 1.0 -qmax 1.0 -i <input_file> -vcodec mjpeg -acodec pcm_s16be <output_file.mov>". Both have comparatively moderate performance requirements. Still, working on a fast Dual Core or Quad Core machine under 64bit Linux is a good idea.
Otherwise, you could transcode your video to MPEG/MJPEG with very low bitrates (but the same resolution), edit, quit OpenShot, swap the files with high quality files that have identical file names, reopen OpenShot and render your edit. (This is what is called "proxy editing".
The only Linux video editor that internally supports editing proxies is the Sequencer of Blender. I confess that I have been too intimidated by Blender's interface to use it productively (although I have used Cinelerra quite a bit...) so, yes, my comments on Linux video editing might have a big blind spot.
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