Just bought a 2012 MBP 15 and need to upgrade the memory to 8GB. Already put in a M4 256GB SSD in it. I mostly use it for work (basic office tasks, Excel/Web/etc) and run W7 through Parellels. Would 8GB be enough or should I consider upgrading to 16GB and make it future-proof? What'd be cost difference? I remember buying 8GB for about $40 for 2010 MBP I used to have.