For an Imac 27" 3.06GHz (DDR3) late 2009 - adding RAM

For an iMac 27" 3.06 GHZ (DDR3) late 2009 can I add a pair of 2x4GB RAM to the 2x2GB RAM that I already have installed (for a total of 12GB RAM)? They are matched pairs - I'm just not sure if each card has to be the same amount of RAM - in other words stick with 8GB or move up to 16GB.