Please ensure you lag from recording is actual lag and not just the software capping your frame rate to record. If you are gaming at over 60fps then the recorder drops you do 30(to keep the files sizes down to about 2 and change gigabytes per min[1920 x 1080] if I remember for fraps) you are going to feel the slow down.
The best performance option is a dedicated hardware compression capture card. The quality may not be quite as good, but the files are MUCH smaller(meaning the hard drive does not have to be as fast or have good access times) and the cpu does not have to do any of the work.
If you happen to have an Nvidia GTX 650 or newer(or was it 650 ti) Nvidia will be releasing an update in the future that will bring hardware accelerated recording of video games using the gpu's build in h264 encoder. This will result in all the benefits of the hardware capture card, but without needing one.