This system was built to handle 4K gaming and streaming, plus also video and photo editing workloads, on a budget of ~$2000.
The GPU was an easy choice.
The RTX 2080 delivers an ~60fps experience at 4K on high settings in recent graphically demanding games. It costs significantly less than the only-marginally-faster 2080 Super (at least here in Australia). It costs more than the 2070 Super, but offers some extra grunt that's very welcome at 4K. Overall, it was the best balance of price and performance at the time.
The CPU choice was a bit more difficult.
Gaming at 4K is overwhelmingly GPU-bound, so CPU choice was not much dictated by this task. Streaming and video editing both benefit from higher core/thread counts. Photo editing not so much, being more sensitive to single-core performance (frequency and IPC).
Intel's i9-9900K would be ideal, a have-your-cake-and-eat-it-too combo. But price was prohibitive, especially factoring in platform cost (motherboard and cooler as well as CPU itself).
AMD's new Zen 2-based 3000-series was extremely tempting, especially the Ryzen 7 3700X, though again, pricing counted against that option: the 3700X is good, but the previous-gen 2000-series parts are too, and those are now a lot cheaper.
So, in the end, the Ryzen 7 2700 won, for much the same reason as the RTX 2080, i.e. offering the right balance of price and performance, across the various use cases and compared to the other available options.
The 2700 can run comfortably on a B450 board with decent VRMs like this ASRock model. Even the Ryzen 9 3900X can run fine on the older B350 version of this board, so no worries with this board. Two m.2 slots and four DIMM slots are both nice features at the price point too (the latter makes adding more RAM if wanted/needed an easy upgrade).
As for the rest of the system, the main thing to consider was the storage setup, in particular for video editing. Getting the project files and media cache off the OS drive is important. So, in addition to the Intel 660p (for the OS, programs, and games) and the 1TB hard drive (for mass storage), I included another SSD specifically for that: Crucial's BX500 is a decent budget SATA model, which is enough for these purposes.
RAM was a 16GB kit of Flare X, and it ran happily at its rated 3200MHz after simply enabling XMP, which was nice.
Power supply was a solid quality Corsair unit. 650W is plenty for now, and provides headroom for future upgrades.
The Thermaltake case needed some extra cooling, as the GPU heated things up a bit, so I added a 140mm intake fan, which helped. (That's what I like about this case, is that it's cheap and adequate at stock, but offers plenty of potential for upgrading the cooling if necessary thanks to the mesh front.) Building in it was straightforward. Cable management isn't too arduous. Well-placed cutouts make front-side tidying very easy.
As for performance, check test results in the pics. All testing was done at stock/auto settings aside from enabling XMP, so there's potential for more performance to be extracted by OC'ing CPU, GPU, and RAM.
Overall, I think this is a price-to-performance powerhouse and I'm happy with how it turned out. Let me know what you reckon below, or over on Facebook where I'm Sensible Systems.