Yes, you can stream to Twitch in 1080p while playing games at ultra settings.
Yes, you can stream to Twitch in 1080p while playing games at ultra settings.
I suggest watching at 720p, honestly. The main issue is that without a sufficient number of viewers, people will only see the source quality. Streaming in 1080p might be harder for some due to poor internet connections compared to 720p.
Perhaps 720p at 1800 bitrate would work. Anything more could cause your internet to slow down significantly.
Upload speed isn't sufficient for 1080p. Your system is fine for Ultra and 720p30/60. For stable 1080p streaming you'll need around 8mbs. Keep in mind you must be a Twitch partner to access the quality switch feature, or viewers may not be able to watch due to insufficient download performance.