The charts are ordered by render speed. For statistical reasons we exclude the most obvious outlier and cards with 12 or less observations. For CS6 we use at least 4 observations currently. Still the results can be misleading due to small samples, so interpret with care.
CAVEAT: A higher gain value does not by definition mean better. It can be influenced by a slower CPU, single processor and/or slower memory. Average render speed may be a better indicator of performance.