My MKIII/060 was over clocked at 66mhz and would do a playable 16-20fps on a PicassoIV at 640*400, if I recall correctly. (It's been several years). I think when I tried 600*800 it dropped to about 6-8fps. If you're only using stock video, I don't think it's going to do well for you.
Plaz