So I have the 27" iMac 27" on it's way. I went with the 8GB standard (plus fusion). My initial impression is that the computer only takes 2 RAM cards, but now I understand it'll take 4. Am I ok to just add the 2x8GB Crucial to the existing 2x4GB, or am I better removing the 2x4GB and keeping the RAM all the same, or possibly ordering another 2x8GB kit to have 32GB total? Thanks!