Nice combo for a good price. Intel i5-8600K is on sale now at Newegg and paired with CM MasterLiquid 240mm liquid RGB cooler combo offers additional savings. If you count CPU at $240 then you get that cooler for just $34 after rebate. ML240L is a nice unit, easy to install, it performs very well, usually allows overclocking to around 4.7-4.8GHz with temps below 60-65C loaded for i7-8700K, with 8600K should be even better. RGB works with or without motherboard headers (in-line control included).
$283.98 - $10 rebate = $273.98 with free shipping
Intel Core i5-8600K Coffee Lake 6-Core 3.6 GHz (4.3 GHz Turbo) LGA 1151 (300 Series) 95W BX80684I58600K Desktop Processor Intel UHD Graphics 630, Cooler Master MasterLiquid Lite ML240L RGB AIO CPU Liquid Cooler
$10 rebate for the cooler:
Combo should be valid for another 3 days I believe.
8600K is pretty much the same as 9600K, the latter does not offer much more than extra 100MHz which is irrelevant after overclock.
Pairs nicely with MSI Z370-A Pro for $80 AR:
And 16GB DDR4 3000MHz G.Skill RAM for $110: