This site
http://radar.weather.gov/Conus/full_loop.php
takes 12 seconds to load and then 2 minutes and 40 seconds to complete rendering.
This Safari problem has existed since the transition from Safari 2.x to Safari 3.x and now into version after version of Safari 4.x
The result is jerky scrolling because of delayed user input, a delay of nearly a second.
This same site will render and animate with FireFox before you can get your finger off the mouse click.
I believe Safari has a core design issue for this problem to remain after 3 years of nightly builds of WebKit and several releases of Safari.
Please try this site and report your findings to Apple.