i5 8400 vs 8600k from a 6600k

Solution
WIth a GTX1080, I'd opt for the 8600K if the 8700K is not viable...

Given any "K" model CPU, the Z370 (Z390 coming) will not aonly allow overclocking, but also allow MCE enabled (full turbo across all cores instead of a single core), if temps are within control. (Add $90 for a Noctua NH-D15 *if* it will fit in your case!)
WIth a GTX1080, I'd opt for the 8600K if the 8700K is not viable...

Given any "K" model CPU, the Z370 (Z390 coming) will not aonly allow overclocking, but also allow MCE enabled (full turbo across all cores instead of a single core), if temps are within control. (Add $90 for a Noctua NH-D15 *if* it will fit in your case!)
 
Solution