After researching the difference between the standard 5870 (ZNF9) and the XXX (ZND9) version is seems the only difference is slightly higher clock speeds (core/memory) on the XXX version. I was curious if in the opinion of the forum members if this was worth an additional $30 which is the cost difference at Amazon.
personally I wouldn't pay the extra for the overclock, I think its generally believed that the factory overclocked cards can overclock more than the standard cards, but I have a standard HD5850 and it overclocks ALOT (From 725/1000 to 925/1125 with stock volts).
You could easily overclock a standard 5870 to XXX clocks. Thats why I think it isn't worth it.