Hi, I have a iMac 20" Late 2006 which has a 2.16 GHz Intel Core 2 Duo. Since installing Lion, the computer is creaking a little, and seems to of slowed down, quite noticable. The system profile says I have 2.5GB of RAM installed. Would upgrading the 512MB RAM to another 2GB RAM make much of a difference? If so, it says it accepts 667 MHz DDR2 SDRAM memory module, could you recommend which is best and where to buy it from? I did do a Google search for 667 MHz DDR2 SDRAM memory module, but found thousands of different types from different companies, are some brands better than others?