Hi all - new to the forums as looking to get some answers on RAM upgrades! I own a mid-2011 27" iMac, 3.4 GHz i7 AMD Radeon HD 6970M 2048 MB graphics, and 1TB hard drive. I am looking to upgrade the RAM from the present 2x2 GB 1333 MHz DDR3 and going up to 16gb or possibly even higher. I was hoping you guys could answer a couple of questions. Is it possible to simply use 2 x 8GB of ram, or do I need to spread the 16GB across all four slots, so 4 x 4GB? Also - I have read a few examples of folks using DDR3-1600 rather than DDR3-1333. How safe is this? Also - is it possible to go higher than 16GB on this model? And do all allocations have to be even? So could I house 2 x 4GB in the top slots, and 2 x 2GB in the bottom for example? I hope this all makes sense! Being a relative newcomer to the mod side of things I was hoping this would be the place for clarification. Thanks in advance.