I'm looking to upgrade both my Macbook Pros (Late 2011 and 2009 13 inch) and my mid 2010 iMac from 4gb RAM to 16GB RAM. I want the best possible because I'm a video editor and have photoshop, premiere and loads of other stuff on at the same time. Price limit of around £150 for the RAM. I think they both support 1333MHz but wouldnt mind getting 1600MHz. Also, what are the consequences of upgrading to 16gb? Shorter life time? Does the iMac have to have 4 4GB sticks?