My 8 drive RAID array is a little weird. Throughput is decent, but latency is kinda bad. This causes World of Warcraft for mac to not be able to keep up when capturing in-game video at high data rates (200+ MB/s), which of course is the only way to get large frame size *and* high frame rate :) It took me literally years to finally think of this solution, and after a lot of fine tuning, it works great! The basic idea is to capture video files to a ramdisk and continuously move them to my RAID array during capture. See the script comments for the gory details.
https://gist.github.com/dreness/7293462
Here is an example use of this fancy fast capturing in action. These clips started off as 1920 x 1200 @ 100 fps, which is about 300 MB/s during capture. FCP X was used to re-time the clips and export for YouTube.