I use this fantastic website: https://www.userbenchmark.com/
It compares multiple benchmarks from people's rigs all over the world, and is the most accurate component comparing website I know. You can compare GPUS, CPUS, SSD, HDD, RAM, and USB devices. You can also benchmark your entire system here and compare it to others with the same specs.
It includes details like percentiles and percentage performance compared to others. It also includes popularity and sales stats.
This should hopefully help you make your decision and give you more piece of mind when it comes to picking PC parts.
To answer your question also, the RX 580 is better than the 1060 3GB. Not only does it have much more VRAM (which is great for future-proofing), it...