Go to http://dglazkov.github.com/performance-tests/scroll-by-hiding-tables.html, click "Go", then check/uncheck "User overflow:hidden" to see the difference in FPS. Compositing shows the biggest hit: Check "Stacked tables using z-index", "Use overflow:hidden", then "Go", then check/unchek "Use compositing."
Wayback Archive: http://web.archive.org/web/20140805121839/http://dglazkov.github.io/performance-tests/scroll-by-hiding-tables.html