Each 7870 is using the same chip and boards. Ditto for GTX660 They may differ a bit based on the amount of factory overclock.
Each is marketed with fancy coolers in an effort to fetch a premium price.
Are they worth much? Perhaps not. The big coolers get heat off of the gpu die well, but they dump the heat back into the case.
Direct exhaust blower type coolers may not be as efficient in cooling, but they get heat more directly out of the case.
And, you may have a preference for some brands, or like the drivers from one better than the other.
In the end, they are more alike than different; you mostly get what you pay for.