The first digit in the model number is the generation, so the 4th generation is newer and generally more efficient than the 2nd and 3rd generation cards, but with the variation in memory and configurations just being newer isn't enough to make it better than previous cards. A vehicle made in 2010 is generally going to be using as good or better technology than one made in 2005, but a low end 2010 car is not going to out perform a mid or high end 2005 car.
The next 3 digits give the relative ranking of video cards, so the 4350 is ranked lower than the 2600 or 3850.
