If you're streaming to Twitch, go with 720p, 30 fps, 2000-2500 Kbps. If you insist on 60 FPS go with 720p and 3000-3500 Kbps. A high motion game like Overwatch will look like hot garbage at 1080p60 regardless of your settings due to Twitch's bitrate limitations.
If you're streaming to Youtube, set your encoder to QSV and throw 9000-12000 Kbps at it if you have that much available.
Enable vsync or the frame rate limiter in the game regardless of where you stream to.
Lastly, update to OBS Studio. OBS Classic is no longer in development.