it depends on the resolution and frame rate you're trying to capture
capturing 1920x1080 @ 30fps will push the cusp of 50MBps write speed, but I really wouldn't want to record to the same drive as the OS and/or game install (unless it was solid state, although I wouldn't necessarily want to record to SSD either for other reason).
I run my OS off my SSD and a few of my primary games, and then I have a separate drive for all my other games and some RAID0 setups for video captures.
capturing 1920x1080 @ 30fps will push the cusp of 50MBps write speed, but I really wouldn't want to record to the same drive as the OS and/or game install (unless it was solid state, although I wouldn't necessarily want to record to SSD either for other reason).
I run my OS off my SSD and a few of my primary games, and then I have a separate drive for all my other games and some RAID0 setups for video captures.