I've settled on getting a refurb 13" MBA because I'm sick of replacing my PC laptops every 2 years (like clockwork!). The question: what do I need memory-wise to make this truly an upgrade for me? I'm currently using an Acer 560G-SB448, running Windows 7 with 6 GB of RAM. I find it does lag when I have too many browser windows open, or when I'm editing photos in Lightroom. I don't use it for anything more ambitious than that. According to most of what I've read here, I still qualify as a light/normal user and 4 GB of RAM would do me just fine. Does 4 GB on a MBA take me farther than 6 GB on a PC, or am I right to be tempted by the upgrade to 8 GB? And a follow-up question: what's the rule of thumb for refurb release dates? Is a 2013 worth the few extra bucks over a 2012?