Well, that and 2-4 frames per second on an Iyonix not really being remotely acceptable. That's just raw Flash with no audio playback. Once you add in audio support, you can expect things to be slower. Flash video is another kettle of fish entirely. All of the above is why I've not bothered touching the Gnash port for over a year.
Oh, I guess not having a working RISC OS machine probably has something to do with it, too