IMO, That guide is awful if you want a high quality local recording. The bitrate is only 1000 which is insufficient . Couple the low bitrate with a "ultrafast" preset, there is bound to be some serious quality degradation.
The guide also talks about setting custom CRF values but that wont make a difference when using a max bitrate of
1000 because it doesn't give the encoder enough headroom to use a higher bitrate to achieve a higher quality level.
In response to the OP, as you must have figured out from the above comment, pixilation is caused by using a too low bitrate. Using a low bitrate means the x264 encoder cannot maintain a good level of quality.
I've been using these settings for my local recording and the quality is superb and there is minimal impact on the CPU. Of course, if the output file is too big, you only need to increase the CRF Value or encode the ouput video file using software such as handbrake to a more appropriate size.