I don't know if it's supposed to be like that, but when recording at 1080p60fps (video quality on "High") and using AVI instead of MP4 the video bitrate is at 3.9 MILLION kbit/s (audio at 1411 kbit/s). My 54 second test recording is 1.59GBs big.

Yup, it's now 60k for "Ultra" and 30k for "High", even better than I expected. Thanks alot!

Sorry for taking so long to respond, I totally forgot about it.
I was recording at 1080p60fps using MP4(Intel Quick Sync).

How can I improve the video quality further? I found the options and set it to "High" and the bitrate to 100%, but the bitrate is only at about 8000 which is not enough for fast paced shooters.