It's also worth noting that the electrical performance of your cheaper card's chip may not be as good as the higher grade chip, so may overheat more or have a failure earlier in it's life.

On chip lines like these, there's usually a process called "Speed Binning" where basically when you test the performance of each chip, and you put the higher performing ones in a different "Bin" than the slightly less efficient ones. You then sell the super high performance ones for a higher price, or put them in the more expensive product lines, as they will be less likely to fail.

i.e: Of all the chips that don't fail their tests and are rejected, 85% are of C grade performance, 12% are B grade, and 3% are A grade. Intel does this to get the "Extreme Edition" chips, and i'm assuming Nvidia does this to select the chips for their higher grade product lines.