Video settings:
Canvas size: your monitor (1920x1080 or whatever)
REscale size;1920x1080
Filter bilinear,
FPS 30 or 60.
Output:
Stream section: RESCALE to 720p
Record section DO NOT RESCALE
You will record 1080p and stream 720p.
You are encoding video 2 times, so you will need a poweful CPU if you use x264 or a powerful GPU if you use NVENC, AMD AMF or Quicksync.
Or you can record with your GPU and stream using CPU x264 to balance load.