I recently upgraded my system. I went with an Intel Core i7-8700 (not the K version), ASUS Prime Z370-P motherboard, 16Gb RAM (will upgrade to 32Gb later), a Samsung 500Gb SSD for the C drive, Windows 10 Pro 64-bit. Since I run four monitors and do some video work, I also added a Gigabyte GeForce NVidia 1050Ti 4Gb graphics card. I replaced the stock CPU fan with a CoolerMaster Hyper 212 Evo from my old system. It's very quiet and more than adequate for the i7. The stock fan might have worked, but I've had overheating issues in the past so felt more comfortable replacing it. I put all the guts in a Corsair Carbide Series 100R Silent Edition Case.
This system is smokin' fast and reasonably quiet. The only time I hear the CPU fans really kick in is when I'm rendering video. Otherwise, the processor barely ticks over. The Corsair case isn't truly silent, but it's definitely quieter than your average gaming case. Everything fits inside nicely. The fans are decent and the sides have noise-reducing baffles. On the outside, it's just a big black box, which is exactly what I want. I don't need a carnival light show under my desk (I've got more than enough of that in my studio). I needed more USB ports, so I added an 8-port front panel hub, and two back-panel inserts.
One "gotcha" to watch out for with this motherboard/processor combo is the C-State setting in the BIOS. It must be disabled, or your processor will think, "Gee, if nobody's going to challenge me I'll just take a little nap." It's supposedly a power-saving feature, but it makes your DAW run like crap. Once disabled, everything runs like an champ.
I managed to get most of the components on sale. Windows 10 was free (I signed up back when Microsoft offered it), and I used most of my old hard drives, monitors, mouse, keyboard, etc. So the basic system came in under $1,000. Of course, that's not counting a new audio interface, fourth monitor, Slate Raven, and other odds and ends. Add all that up, and...well, I don't even want to go there. But the core system was pretty reasonable. If you don't need such a beefy video card, you could build a fantastic system for under $800.
I could have gotten the i7 8700K for a little more, but I don't feel overclocking is necessary. It just uses more power, requires more cooling (thus more noise) and potentially shortens the life of the processor, all for a negligible performance gain. The standard i7 8700 is lightning fast and plenty powerful without overclocking. I do look forward to upgrading the RAM to 32Gb though.