To HD or not to HD?

[outlawed]

As for playback issues. You're forgetting the myriad issues of:
OS, graphics card/drivers, memory, and media playback program which will all greatly affect the ability to play back high res video files (codec not withstanding). There is more to it than just raw CPU load.

As far as the editor effort aspect....HD isn't worth it unless you are working from Bluray source. But if you have a turnkey system and can easily convert from a 720p transport stream to our editing bay then by all means feel free =p