My main rig is an i5 6600k with 32G of RAM, GTX 1070, 240G boot SSD, 3TB HDD, running a 4k60 Dell 27" monitor, a 24" 1080p Dell, and an Asus 1080p 24" “EVO monitor” (low-latency TFT display for dedicated gaming; it’s actually on an HDMI switch so I can use it for consoles as well). Thing’s used pretty much exclusively for gaming, with occasional development work when I need to build something for Windows (I’m a Mac user normally).
Last year I built a dedicated streaming rig to help run my charity marathon stream (previously used other peoples’ computers for play, and my gaming rig to run the stream) based on a refurb’d server mobo – Intel S2600CP2J w/ Dual E5-2670’s (each 8-cores, plus HT), 128GB EC RAM, 120G boot SSD, 8TB HDD, and my old GTX 970. I’m gonna toss another couple HDD’s in there and spin it up as a VM/Containerization machine when it’s not streaming.
For video capture, I have 2xAvermedia C127 Game Broadcaster HD’s, 1xBlackMagic Intensity Pro, and 2xBlackMagic Intensity Pro 4k’s. They move around between the two machines as necessary, but the BMIP4k’s and C127’s are likely to stay in the streaming rig once I re-case it.