Hi, I'm looking to upgrade the RAM in my 27" iMac, but am not sure if i have selected the correct RAM. Could someone help clarify this is correct? My iMac is 'Apple iMac (21.5 and 27-inch, Mid 2010) Desktop/PC'. The RAM I have selected on the crucial website is: 8GB Kit (4GBx2) DDR3 PC3-10600 CL=9 Unbuffered NON-ECC DDR3-1333 1.35V 512Meg x 64 Part #: CT3309321 Am I correct in saying that you can mix and match RAM. e.g have 2x2GB and 2x4GB making 12GB total?