I just ordered myself 16GB (2x8GB) or RAM for my iMac. It currently has 4x2GB installed for 8GB total. I was just going to take all the current RA out and put the two new sticks in but I wonder if I can add up to the unusual amount of 20GB of RAM by leaving 2 sticks of 2GB in the top slots and the new RAM in the bottom slots. Both should remain dual channel so no issue there right? I ask purely because, in theory, it should work however I know RAM amounts usually follow specific trends (2, 4, 8, 16, 32, etc) so I was just wondering if having a number like 20GB would be an issue at all. Lastly, assuming it's not an issue, which RAM should I remove? The factory default 4GB or the 4GB I bought from OWC myself? P.S I am aware apple says that the 2011 iMacs can only hold 16GB but I know for a fact that they can hold 32 so I'm not worried there.