If you want to stream at 1080p 60fps, I would advise YouTube as they recommend 12 Mbps for that while
twitch restricts you to 6 Mbps which is what YouTube advises for 720p 60fps. You can also add a static border where ever possible. The more static content, the more bits for the dynamic content.
Choose a quality that will result in a reliable stream based on your internet connection. Read this article to learn how.
support.google.com
For recording, they also recommend 12 Mbps (but VBR). For recording, most people recommend recording with CQP rate control (AMD might call it something different) where you pick a quality level instead of a bitrate.
These features are only available to partners who use YouTube Studio Content Manager. Below are recommended upload encoding settings for your videos on YouTube. Container: MP4
support.google.com