Ideally your frame rate should be set at 29.97, or you could set it to 30.
If your encoding computer's CPU is overloading you could try adjusting your frame rate to a lower value (25, 24, 20, 15, etc.). Reducing the frame rate may also allow you to broadcast at a larger resolution with a lower upload speed. Do keep in mind that lowering the frame rate may work well for your broadcasts, however they may not "feel" as smooth as the higher frame rates depending on how much motion you have in your broadcasts. If needed, experiment with your broadcasts to see if adjusting the frame rate works for you.