NVIDIA GeForce GTX 1660 Ti OpenCL Benchmarks, 14-Way NVIDIA/AMD GPU Compute Tests
ROCm OpenCL wasn't working for the Darktable RAW photograph software, but of the GTX 1660 Ti performance against the other NVIDIA GPUs you can see its performance was in line with the other Pascal GPUs and not quite the RTX 2060/2070.
With clpeak's OpenCL global memory bandwidth benchmark, the GTX 1660 Ti with its GDDR6 video memory came out 9% faster than the Radeon RX 590.
The Radeon consumer GPUs do much better with the single precision float test of clpeak where the RX 590 was performing in line with the GTX 1070 Ti while at least the GTX 1660 Ti had a 40% boost over the GTX 1060.
The Radeon GPUs with the ROCm OpenCL stack are working out very well these days with the double-precision compute performance.