Intel is making its recently launched Skylake-X HEDT platform look even more ridiculous, but for consumers and gamers this is all good news. Coffee Lake is basically Kaby Lake with more cores, and manufactured on the slightly more optimized 14nm++ process. The biggest downside is that you will need a new motherboard, Coffee Lake only works with a Z370 motherboard.
Lets take a look at some reviews so see how Intel's latest mainstream processors perform. The Tech Report tested the Core i7 8700K and writes that this processor offers world's best single-threaded performance, multi-threaded performance that matches the AMD Ryzen 7 series, and good overclocking. The reviewer concludes the 8700K has virtually no weaknesses and is the easiest Editor's Choice pick he has ever made.
A second opinion can be found at HotHardware, they checked out not only the Core i7 8700K but also the Core i5-8400. The verdict is both parts perform well. The Core i7-8700K is faster all-around than the 7700K and competes well against AMD's eight-core Ryzen 7 in terms of multi-threaded performance. The Core i5-8400 is a compelling sub-$200 part, it's sometimes faster than the 7700K but its multi-threaded performance isn't on-par with six-core Ryzen processors. You can find links to other reviews in our Mailbox section.
Word on the street is that availability may be a bit of a problem the coming weeks/months. A quick check at Newegg reveals the 8700K costs $379.99 and "usually ships within 15-20 days". Amazon doesn't even list the product so it is indeed a very low volume launch. Newegg does seem to have the Core i5-8400 in stock though, you can buy it for $189.99.