I was thinking of adding memory to my 8gb iMac. I use up memory pretty fast when I run Parallels. It's a 2.7ghz Intel Core i5 and the memory consists of 2 4gb 1333 mhz ddr3 chips. So I'm thinking Apple must sell the memory, but I couldn't find it on their website. I did a google and window shopped at macmemory dot com. I can get 2 8gb modules for $179. So I'm wondering several things: 1) is that a good price; 2) macmemory a good store? 3) can I mix memory module sizes? There are already 2 4gb modules in the system, can I add 2 8gb modules? The memory they are selling is This just a bunch of sales BS or is it important? I appreciate your advice.