6th Generation Skylake Motherboard Recommendations (non-overclocked)

ah, ok. I see what you are asking.
This is posted on the website you linked for the specs.

1 x M.2 x4 Socket 3, with M Key, type 2242/2260/2280/22110 storage devices support (both SATA & PCIE mode)*1

*1 When the M.2 Socket 3 is operating in SATA mode, SATA port 1 will be disabled.

So if you are putting an M.2 drive in there, and it's a powerful one that can run in PCIe mode, then unless you've got a million PCIe addons taking up slots and using lanes then just run it in PCIe mode. Alternatively, as it states, it will use the SATA 1 port for it which to my knowledge is a 6GB/s port and most SATA SSD's only require and run in 3GB/s mode so you're not missing out there. In fact, the board has 6 SATA ports on it that run up to 6GB/s so like I said, if your M.2 drive is an NVME drive or similar that can get a speed boost from using PCIe lanes then you can let it run in SATA mode. Or, if you have 6 devices total (whether it be an SSD, HDD or some other device that connects using SATA) to take up those ports then you'll run it in PCIe mode as well.

Also, you won't be running unstable if you overclock. Only if you overclock to an unstable level and keep it there. I have my CPU overclocked to 4.6Ghz because that's where it stays stable. (It actually goes to 4.7Ghz stable but it just runs a little hotter than I'd like it too). It's not unstable in any way and I keep my PC going 24/7 for the most part. As long as you don't try to go beyond a CPU's limitations and try to keep it there and have appropriate cooling solutions then you are golden. But with my OC I am getting the performance that I paid for in my CPU, because, if it can go there, then why am I not putting it there? It's extra performance at no cost to me. Sure, it'll put a little more strain on it's lifespan but the difference is so little that it doesn't matter, like, as an exaggerated example, without the OC it would last for 20 years, but with the OC (and of course proper cooling to keep the temps down cuz that's what'll kill it the fastest) it'll last for 17 years. But in the short term, those numbers are small and in the long term, well, I'm not gonna keep a CPU for that long.