Games play fluently on a computer anywhere above 60 fps, in general it's the higher the better, especially on shooters. Most shooterplayers prefer 100+

If you use FRAPS to record it locks the game's framerate to the recording framerate, therefor you want it as high as possible and at least 60 fps.

If you use FRAPS to record 60 fps, the game will run at 60 fps (if your pc can handle it o/c). If you turn it down to 25 fps for "more" performance (considering harddisk), it'll instantly drop your gameframerate to 25 fps and the game will start to feel laggy.

Yes, some games do have the possibility to make a demo, that you can playback later. For example Call of Duty 4. In that case, I prefer to replay the demo and record it at normal framerates. My next gaming video will be made this way on call of duty 4. The plan is to have all people in a server record their own demo's on the same game they play together, and afterward record all points of view to all the action and using that to edit and make a high quality movie for our website.

I hope I explained it well, feel free to ask, I 'm quite experienced when it comes to gaming and PC performance, just dropping in here to get more video-editing knowledge for video made with a camera.