The 860 is m.2 SATAIII so its no faster then a normal SSD. The 970 is a m.2 NVME that uses PCIe lanes, much much faster then SATA. For gaming and most other non professional tasks, you wont ever get close to the full potential of the NVME drive, so save your money and get the 860. Its still loads faster over a traditional HDD.
If for whatever reason you do want the 970 ensure your motherboard supports it as some are simple SATA m.2.