Stream settings?

Hi there, so I just got myself a new PC and I've always wanted to stream, (Just my previous PC wasn't good enough too..) and my new PC's specs are: CPU: I7 7700K GPU: Gigabyte Nvidia GTX 1080 GDDR5 8GB OC WF3 PCI-E HDD: 2Tb Seagate SSD: Samsung 850 EVO 250Gb PSU: EVGA 650w CPU Cooler: Corsair H100I V2 RAM: Corsair Vengeance 16Gb (2x8Gb) I was just wondering what kind of settings I should be running with this PC? My upload speed is 5Mbts and so I've got my current bitrate at 3000 (Streaming on twitch, so there's a limit) But I just want to know, should I be streaming at 1080 and downscaling to 720 or not downscaling and just at 720? Should I use software encoding or hardware? What am I capable of streaming at (1080p60, 1080p30, 720p60, 720p30)?