GeForce GTX 1080 's Advantages
More VRAM (8GB vs 6GB)
Larger VRAM bandwidth (320.3GB/s vs 192.1GB/s)
1152 additional rendering cores
GeForce GTX 1660 's Advantages
Released 2 years and 10 months late
Boost Clock has increased by 3% (1785MHz vs 1733MHz)
Lower TDP (120W vs 180W)