First and foremost, why are you working at 23.976 and 59.94 fps if you live in the PAL side of the Earth and your goal is just to upload your video on YouTube? Isn't it better start from proper sequence settings?
Secondly, set Bitrate Encoding to VBR, 2 Pass so as to benefit from better quality out of smaller file size.
Regard to bitrate settings, it depends on how you plan to watch the video. If your media player can't play it back in real time, start to gradually desrease it. Keep in mind, modern AVCHD camcorders shoot with 28 Mpbs, first AVCHD cameras shot with 17 Mbps, H.264 YouTube preset offers 10 Mbps, H.264 Vimeo preset - 8 Mbps.
Rather turn 'Use Maximum Render Quality' off. See e.g. this thread.