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What kind of graphics card do you have? I have an AMD 270x and I use AMD Gaming Evolved Raptr with its recorder. It does not impact my FPS and I record at 2560x1440p. It generates huge files on my SSD 2GB for 20 minutes of game play. It also depends on the game though, and your quality settings. I set my quality to 720p.
If you use Nvidia, which I have little experience with, you may want to use OBS as others have suggested. Figuring it out takes a little work. I tried it, did not like it and I stuck with Raptr's twitch and and Game DVR capability.
On another note, we all know you use sneaky Irish hacks - no amount of video can prove otherwise. HAHA . I do hate your smart kills, when I think I am well hidden you like a fucker will out smart me. It's fun playing with you and against you.