How decide between 13 & 15 inch rMBP based on relative power

[jennyp]

You should also think about an egpu for extra pdf-action.

What is this egpu you speak of?

 

[Meister]

That's just not the case in my experience. When, for instance, I annotate such large PDFs (by highlighting certain passages etc) on my iMac (3.4 GHz Intel Core i7, 16GB RAM) it takes a fair time for them to be saved to their new state. Perhaps the 15-inch rMBP will cope better.

And why is that ram related?