No, LCD bandwidth is not a limitation for low to medium resolution videos. There is no need to downscale them that much. In the worst case, if you hit LCD bandwidth limitation, you will just see tearing and have a noticeable amount of frames dropped, but nothing too critical that would make video completely unwatchable (for example, even dropping framerate to 15fps, video may remain watchable). But if CPU is the bottleneck, video playback will completely stall or regress to showing frames just occasionally, making watching video impossible.