Both nVidia and ATi/AMD cards mention both the Generation and the target performance segments in their model number. Nvidia uses 3 digits, while AMD uses 4 digits currently.
For nVidia
------------
First number is generation, last 2 numbers give performance segment.
Eg, Geforce 610 = 6th Generation, 10 = Lowest performance card in this generation.
Geforce 630 = 6th Gen, 30 = Low Medium performance
Geforce 650 = 6th Gen, 50 =Upper Medium performance
Geforce 660 = 6th gen, 60 = High performance, and similarly
690 = Extremely high end card of 6th generation.
For nVidia
------------
First number is generation, last 2 numbers give performance segment.
Eg, Geforce 610 = 6th Generation, 10 = Lowest performance card in this generation.
Geforce 630 = 6th Gen, 30 = Low Medium performance
Geforce 650 = 6th Gen, 50 =Upper Medium performance
Geforce 660 = 6th gen, 60 = High performance, and similarly
690 = Extremely high end card of 6th generation.