The information in the "fastest GPUs" page is "transient"... it considers only recent data, is frequently changing, and can be perturbed by MANY factors. For example (just one): if you run two simultaneous jobs on a single GPU, their run-times may be twice as long, but the stats have no way to distinguish that.
General rules of thumb:
For Genefer, the Nvidia TITAN and the top-of-the-line ATI(AMD) cards rule the roost. Beyond that, probably the Nvidia 5xx series are fastest (especially the 580). Nvidia lobotomized double-precision performance with the 6xx series and later to protect their (very expensive) Tesla market.
For PPS Sieve, Nvidia cards are by far the fastest (DP float not required), at least for the mid-range cards on up. One must learn to read their branding: the first digit is the generation, with higher numbers being more recent. The second digit reflects (usually) the computational power relative to the generation. I have a 770 and it is roughly equivalent to a 680. AMD cards perform relatively poorly on PPS Sieve.
I've made some generalizations here, and given only a couple of examples, but hopefully it's helped to give some guidance. Main thing to remember is that no "one size fits all"; everyone's box will perform differently.