Testsetup being used for the video:
Cat 8.1, C2D E6700 @ 400x8, XP x86 SP2, Gigabyte X38, 2 GiB DDR2-800

The Fps are that low because of AA being used in combination with a high resolution. I didn't make the test myself, so I cannot tell you what exactly has been used. But what you can clearly see is that even 25-30 Fps on UT3 feel way less smooth than the 15 Fps with CF disabled.

We made sure it's not just a weird behaviour with that specific hardware configuration. It's the same on skulltrail, P35 and 780i using completely different components.