At whatGFX we calculate our benchmarks a little differently to other sites to help make the final scores more appropriate to those who want to actually buy the best gaming graphics cards on the market. This table shows all of the reference editions of the graphics cards produced by NVIDIA and AMD ranked from fastest to slowest. While you can't buy the older cards it's still a good comparison.
Our performance score is calculated by adding the results of a couple of software benchmark tools with some of the directly comparable hardware statistics, such as GFLOPs, gigapixels/second, power consumption and a few others. These weighted metrics are tuned to rank hardware specifications over some potentially arbitrary software benchmarks or some of the more esoteric specifications. Effectively what this means is that if you have two reference GPUs with similar software benchmark scores but one has slightly higher reference number crunching ability, we'll rank the one with better hardware on paper on top even if it was missed by the occasionally picky software benchmark suites. Please note that our benchmark may not indicate superior performance for your chosen game or games, it's always worth a second opinion when in doubt.
The second figure is simply a relative performance percentage, the fastest card always being 100% and a performance score of zero being 0% just to give an idea of the performance increases as you look at the faster cards at the top of the table.