I need a low end MBP for my wife. I'm trying to decide between a MBP MD101LL/A or a refurbished MF839LL/A. The MD101LL/A comes with 4GBs of RAM and a 500GB traditional hard drive, BUT it's easily upgraded to 16GB and a super fast SSD. The MF839LL/A features a Retina display and is about 25% faster out of the box than the MD101LL/A, but I'm stuck with 8GBs of RAM and a 128GB hard drive, which means I'll also need an external drive. What would you do?