Thanks for those infos, now if your mainboard supports it you could use Intel QuickSync which would offload the encoding work to your integrated intel gpu instead of running on your processor.
The only alternative I see would be using the ultrafast preset (under advanced settings) to decrease the cpu load, but it will definitely not look too good unless you start using unspeakable bitrates.
Overall for streaming, especially to twitch.tv it is not recommended to go much further than 3000-3500 kbps.