I am not sure what type of performance you are getting overall, but I can say that the site you just linked to is loading over 6 large gifs. The one I pulled from the site is 2.8mb to download and was made up of 106 frames. That is not a small gif, it fact it is massive. Now times that by 6 gifs and that is your problem with loading that page and the gifs. It took my browser time to cache the gif file before it could play it back cleanly. This is the fault of who made the gif not your Mac or the browser. That site was pretty sketchy too. It was prompting me to download Lime player or some sort of player. I would suggest you do a complete reset of Safari and dumb any cached files, history, and cookies. Then restart the browser and try this gif I linked to below. It should play back cleanly. It does on mine. http://dribbble.com/shots/550172-Hypercompact-Animated-3D-Logotype?list=searches &tag=gif
the page you are linking has just one gif playing.
After the first run, the playback is indeed fine.
And I can confirm that it is Safari and not Web-Kit which is having the troubles.
But than again Safari 6.0.5 is fine!
Also fine is Safari 5.1.7 on Windwos.
I'm helping a freind building a website, and after Mobile Safari does not support alpha channels, I advised him to use Animated GIFs.
Sure they could be a bit more optimized, but we are not talking about huge data.