Capturing HD on my Q9650 @ 4ghz barely registers on taskmanager - maybe 2 - 3% max -.. It has to do with I/O throughput rather than CPU ...
Any recent chipset is as good as it gets ..
Video capture as opposed to file transer - say AVCHD from an HD or SD camcorder, is bound by real time .. i.e.. 30 Minutes of video takes 30 minutes
to capture...