In your logfile it shows you have 3 sources in the same scene, 2 of those sources are conflicting for recording/streaming purposes:
18:40:55.145: - scene 'Capture':
18:40:55.145: - source: 'Window Capture' (window_capture) <--- Dependent upon what you set to hook into, may also be conflicting.
18:40:55.145: - source: 'Game Capture' (game_capture) <--- Will record the game you have specifically set to capture.
18:40:55.145: - source: 'Display Capture' (monitor_capture) <--- Will record everything displayed on the monitor you have selected for display output.
You need to re-do your scenes and sources so you don't have any conflicting sources, have the monitor capture source in a separate scene by itself and it should improve your performance a lot.
With your system specs you should be able to record at at least 1080p@60fps with the highest quality settings, if after you have re-done your scenes and sources you are still having performance issues, can you upload another logfile with a fresh recording attempt for further troubleshooting.