I've never really figured out why, but CamStudio and FRAPS kill performance on my machine and tend to skip a lot of frames when recording.

Call me old school but ever since YouTube is able to convert videos from high definition quality to quite manageable formats and sizes, I tend to record my video game stuff with an HD camera.

Then go from there. No slow downs when recording.

If your video card sports a video out you could also just record everything the monitor puts out through that and then edit it to your likings in whatever video app you prefer. This requires a bunch of hardware in most cases though.