Thank you both for your speedy replies..!
The truth is, I have no idea what features I'm going to need over and above any others. On Amazon at the moment, the ASUS is 154€ and the AsRock is 137€.
In January, I cloned Windows 8.1 to my first SSD. It's a 500GB Samsung 850 EVO. I upgraded to Windows 10 , then did a full install. I recently checked Samsung Magician and discovered that the 'Total Bytes Written' is at the 4TB mark. To say I was shocked would be an understatement. If I don't work out what the problem is, I may have to buy another SSD soon..! I don't understand how I could have filled the drive 8 times over in 3-4 months. I think I heard that with AsRock Extreme boards, you don't have to reinstall the OS. With that, the 18€ difference, the great storage performance and the Ultra M.2 slot, I'm seriously considering buying the AsRock. But from numerous reviews (which I spent two whole days reading) of both boards, it seems like the ASUS has much better sound capabilities, stability, overclocking of CPU/RAM. Just seemed like there were more negatives with the AsRock than the ASUS, but the reviews were mostly from 2015, so maybe BIOS/System updates have improved things in the Extreme4's favour since then.
In order to help you help me, the things that may be most important to me for this upgrade are:
1. Not needing to reinstall Windows 10
2. Stability
3. Problem-free storage
4. Whichever board will run this properly
http://www.amazon.it/Patriot-Memory-PV416G300C6K-16GB-PC4-24000/dp/B0157UQ5A6?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
Amazon had a sale 2 weeks ago and I got this 2x8GB 3000MHz DDR4 RAM for 40€. Crazy, right..? Should have bought another set...
Again, thanks for everybody's time on this matter.