I have a mid-2011 iMac and I'm thinking of upgrading the RAM. When I bought the iMac, I upgraded the RAM with Apple to have a total of 8gb RAM. This used up two of the four slots so each slot is worth 4gb RAM in it's current set up. I went to OWC to look into upgrading the RAM and it says my computer may be able to upgrade to a total of 32gb RAM. It also says to upgrade in pairs. My question is, am I able to buy an additional 16gb RAM for the remaining 2 slots? That would mean I would have a 4gb RAM, a 4gb RAM, an 8gb RAM, and an 8gb RAM. I'm asking because I'm wondering if I can mix and match them as I please or do I need to stick with 4gb RAM all the way through?