Benchmarks, lol. Basically the only static thing about video cards is the RAM, but thats such a poor performance indicator that your better off looking for benchmarks.
Core speed, Memory speed, Rof's, pipelines, memory bandwidth, these are just acouple terms used when looking at a video card. The problem arises when you compare two different cards.. Say an 7900gs and a x1950pro. one card may have more pipes, more memory, higher clocks, but it still doesn't guarantee that that card is better.