.but I'm assuming that when I try to overclock the 2 cards (they are same factory clock) , I'd have to do it individually to see what the tolerances are for each card, since they leave the factory different, no matter what factory version? right?
No, I just used RivaTuner on my sig rig and it works just fine. OC's both cards at the same time nicely. You shouldn't run into any problems as long as you don't try doing something like OCing them to 800MHz core with stock cooling. The fan speeds can also be adjusted via RivaTuner.