Unless you plan to use any Amigaoid powerpc system and OS as your only system then you should not use the video playback yardstick as the only criteria. I enjoy my Sam460ex + AmigaOS as well.
Video playback would be seen as this machines weakness. I watch a lot of videos on this machine. I just re encode them to a smaller xvid avi format at high bit rate using a PC and transfer them to the Sam460ex via FTP. Quality of the playback with these is excellent. About 6 Minutes to convert a 45 minute video and can do 5 videos at a time. The default playback quality using emotion video player on the Sam460ex is much nicer than on the basic PC setup.