NVIDIA GeForce GTX 1070 GDDR5X 's Advantages
More VRAM (8GB vs 6GB)
Larger VRAM bandwidth (256.3GB/s vs 192.1GB/s)
512 additional rendering cores
NVIDIA GeForce GTX 1660 's Advantages
Boost Clock has increased by 6% (1785MHz vs 1683MHz)
Lower TDP (120W vs 150W)