Hello, everyone. I have MBA mid-2013 i5/4Gb(First Mac machine in my life)model. I have been using this machine for almost 2 years and it has been doing great. I had some problems before when system just freezes(had to force power-off, nothing works) or that spinning rainbow keep stays for awhile. Whenever this happened, one thing I knew was that RAM usage is almost 100%. Even when I use safari(less than 5 tabs opened), mail, and itunes, RAM usage is almost above 75~85%. I was thinking about purchasing i5/8Gb logic board to upgrade my machine but I'd like to hear from you guys if there are going to be some(doesn't have to be huge) advantages if I upgrade to 8Gb. Thanks.