OpenCL performance is becoming a hot topic for GPUs. We use the free-to-download CLBenchmark and focus on the fluid simulation and image blur benchmarks.
AMD's been a big proponent of OpenCL while Nvidia has been ploughing along with CUDA. The fluid simulation test runs significantly faster on Radeon cards.
Each company picks benchmarks that suit its purpose. All GPUs perform well in the image blur test, though it takes the Tesla-derived Kepler architecture for Nvidia to keep in touch with older-generation Radeons.