The solution to this issue, so far, has been to either use proxies or transcode the clip into a format that can be rendered in real time (ex: ProRes 422). Each of these solutions has a disadvantage. Proxies add complexity to the workflow (I wish Premiere or FCP would handle them like After Effects does) and if you transcode to another codec, you are losing some image quality (they don’t handle the color the same way). The lost might be minimal but it is there. That is why some people just keep editing in H.264 and accept the ever present render bar as a necessary evil.