The title says it all. What's the difference? Is there a slight/moderate/huge difference in speed/battery life performance/etc? And is it worth it? I see a Kingston 8GB (2x 4GB) 1600MHz for $105. I have MBP 13" 2011 Also, a different topic, instead of making a new one. What ram brand do you recommend for 1333MHz? And once I upgraded my laptop ram, can I use (2x 2GB) that came with my MBP2011" to put in my 2009 MacBook? Can it handle 1333MHz?