Enthusiasts who want the fastest possible storage speeds already know to buy motherboards that use flagship chipsets (e.g. Intel's Z370 and AMD's X470). However, a series of benchmarks from TechSpot confirm that dual slot X470 boards can restrict performance if one of the slots is connected to the chipset with PCIe 2.0.
https://www.notebookcheck.net/TechSpot-benchmarks-highlight-importance-of-selecting-the-correct-M-2-slot-for-best-performance.309816.0.html