Rdslw :
http://ssd.userbenchmark.com/Compare/Samsung-960-Evo-NVMe-PCIe-M2-250GB-vs-Samsung-860-Evo-250GB/m200373vs3949
table will show it all. TLDR around twice as fast in most tasks.
This is not actually very accurate. Maybe in some synthetic benchmarks and extremely specialized tasks you'll see a big performance difference, but in most real world tasks they should perform very similar to one another. See this 960 Evo review, for example, where they compare the load times of various SSDs, including the 850 Evo...
https://techreport.com/review/30993/samsung-960-evo-ssd-reviewed/5
Whether it's Windows boot times, application start times, or game level loads, the performance is nearly identical between all the drives tested, and probably within the margin of error on their test system. That's because other parts of the system will be what's limiting performance, such as the time it takes the CPU to decode the files that it's loading. Technically, the 960 Evo might be faster, but you probably won't see much of that performance, making the price premium probably not worth it.