Do you absolutely require every frame as an I-frame? Then just use MJPEG and pick a bitrate/quality if you absolutely have to deinterlace and recompress. If you can deal with, say, every 3rd frame as an I-frame, or every 10th, etc, then you can get huge compression gains by using xvid (EQM UHR matrix, Q2 or 3, no B-frames) and very minimal lag on editing. That's what I always use for intermediates.