Top GPU cards performance comparison in Blender: GTX1080, Titan X, GTX980Ti and AMD R9 - BlenderNation

LionRender have done an in-depth test of four high-end GPU cards.

Home-v4 - BlenderNation

AMD vs. NVIDIA GPU Rendering Performance: Blender, Octane, Redshift & More

GPU rendering - RTX 2080 Ti, TITAN V

NVIDIA GeForce GTX Titan X 12GB Video Card Review

GTX 1080 Blender Benchmark! Finally!

NVidia Titan Xp Review vs. 1080 Ti: $200 Per Percentage Point Gained

NVidia GTX 1080 Ti Founders Edition Review & Thermal Analysis

EVGA GeForce GTX TITAN 6GB SuperClocked Video Card Review

NVidia Titan Xp Review vs. 1080 Ti: $200 Per Percentage Point Gained

GTX 1080 Ti vs 980 Ti vs TITAN X vs TITAN BLACK vs 780 Ti vs TITAN / NVIDIA SPECS & NO BENCHMARK

Nvidia GeForce GTX Titan X Review (Page 22)

Vega 64 - 20% faster in Blender than GTX 1080Ti : r/Amd

Creaturebox Robot by William Oglesby - BlenderNation

GPU rendering - RTX 2080 Ti, TITAN V

Vega 64 - 20% faster in Blender than GTX 1080Ti : r/Amd