right and not unusual   for them to revise a bios on the cards    looking at   what you posted above one card i'll assume is your first older card had the   sc bios on it but maybe the later card came with the  classy bios  as see from the   techpowerup chart   of bios's   or you flashed a bios mod based off the classy bios ???
 
I guess  with the sli set up the card will  sync   to the lowest card  performance  anyway    but maybe  now matching them up  could be for the better  ??   then I gusee luck on how well your sc cards  were binned to hold up to the ''better'' classy bios  being used.
 
also elpida   memory was taken over by micron    so I guess now cards with micron memory is about the same as  elpida   [like most all 10 series , yuck ]   I seen folks claimed they  RMA there cards  because they got elpida memory instead of Hynix or Samsung   ...lol...
 
https://www.micron.com/about/about-the-elpida-acquisition
 
good luck 

Well all the watercooling parts has arrived and it seems as the Hynix one does overclock slight more then the Samsung one :) But it has more coilwhine as well :P
Both cards are now flashed with 84.00.41.00.90 bios "modified from my first card" and running at the same clock 1500/4001 :D
Thanks to watercooling both cards staying at 47°C at 100% load after 6 hour

nice temps.   my hybrid  maintains that  as well hottest I ever got it so far has been 48c .      now with that thermal throttling should be well out of your way 
 
enjoy