A lot worse, but your CPU doesn't take a hit. NVENC doesn't have very good quality at low bitrates, but it's fine for local recording (1080p@15Mbps+) that will be transcoded later.

Here's a comparison video: https://www.youtube.com/watch?v=BV5btdqQfu4

According to this it's almost equivalent when you compare 720p@5Mbps and 1080p@12Mbps, which is way more than most streaming sites will do: http://on-demand.gputechconf.com/gtc/2014/presentations/S464...

NVENC[0] has some comparessions with x264.

In our use case(sports broadcasting, 720p) we found that in reasonable bitrate(>1Mb) NVIDIA HQ quality was virtually the same to x264 faster. (in newer versions of nvenc, they got amazingly better in the last couple of years) When the bandwidth drop you start to see x246 advantage.

[0] https://developer.nvidia.com/nvidia-video-codec-sdk