Hmm, may I ask what type of browser you use? I run some Javascript so usually it's slow when running IE. It's much faster on FF & Google Chrome. Even fast on Safari.
Quite an innovative approach. Though the idea of incorporating animated header looks and sounds cool, it may be a bit heavy on some peoples system. But I presume the audience that you are targeting being game connoisseurs are likely to have systems that can handle that kind of thing easily. So it works and looks great.