I just ordered a 27" refurb and it's coming with 8GB of RAM. I know it's got 4 slots and can go up to 32GB. I assume it's coming with 2 4GB sticks? Does that mean I can fill the other 2 slots with 4GB sticks to go to 16GB, or do I have to get 2 8GB sticks? Also, does the RAM have to match? If so I think I'd probably be able to pick up some in the forum marketplace.