I had very very very bad luck with the "Thermal Interface Material" on the 7700k -- I went through 3 different CPUs until I found one that had stable temps suitable for overclocking. My idle temps w/ no OC was 60-70C, and with the automatic boost clock on the 7700k to 4.8ghz it would overheat and shutdown with just running google chrome.
I finally ended up going with a company that "de-lids" the CPU and installs proper TIM -- been loving the CPU ever since. It cost me an extra $50, which is worth it to me since I overclock as much as I possibly can.
www.siliconlottery.com -- excellent experience there as they guarantee overclocks w/ the chips....if that's what you want to do eventually.
The deals with the 7700k on newegg right now are hard to pass up, though. They have A LOT of 7700k's on inventory when i built my rig back in April -- It was impossible for me to find a CPU that wasn't made after November 2016. Since a bulk of that was made before launch in January, they all likely still have the lame stock TIM -- which is BAD.
Long story short -- be sure you monitor your CPU temps w/ that chip.