I have tried that aswell. After changing to that i had my first computer crash.The log looks fine for the most part. Why are you not using NVENC CQP? Its just like x264 CRF but uses much less CPU because its GPU.
Here is a picture of CPU usage with NVENC CQP20 http://imgur.com/a/HtCV0
And the log file of that recording is in the attachments