You might get 5-10 more fps max in any game. With the heat that comes with dual cards, you usually don't get much for overclocks due to the thermal limits of the top card
the overclock you have is slight, and basicaly download a gpu testing software (kombustor from msi isn't bad) take the memory clock back to 0, and start bumping up the core clock by 10mhz at a time, retesting the gpu's for about 15 minutes each time. Do this until you get a driver crash, then dial the core clock back down by 20mhz from the setting the display driver crashed at.
repeat for the memory clock after you have found your max stable core clock. Don't expect huge gains