3DMark Fire Strike is a showcase DirectX 11 benchmark designed for today’s high-performance gaming PCs. It is our [FutureMark’s] most ambitious and technical benchmark ever, featuring real-time graphics rendered with detail and complexity far beyond what is found in other benchmarks and games today.
It's a mixed bag when we start with the usual 3DMark benchmarks. This GTX 1660 scores less than RX 580 in the 1080p Fire Strike test, but comes within touching distance of GTX 1070 in Time Spy. In Fire Strike Ultra (4K) it bizarrely performs worse than GTX 1060 – I can't explain that one so it is likely just a quirk from the benchmark itself.