I'd like to keep this late 2009 model 27" iMac (11,1) up to date to keep it longer. I was wondering, how many RAM sticks do I have in it right now if I have 4GB? If I upgrade RAM to 16GB, am I allowed to mix? $100 for 16GB ram at OWC website isn't a bad price. Crucial website is showing I have 2x4GB sticks, and can get 2 more for $48. I remember spending $100 for 512MB RAM!