13.3 v 15.4 Looking for fast from the hip advice

[BananaRepublic]

I'm on the brink of buying a either a mac pro 13.3 or a 15.4. I'm looking for best buy opinions on one or the other. I'm going to churn out what my intended uses and other important stuff, briefly.

I am not a professional photographer, but it is in the back of my mind.
I am planning to run PS & LR from the CC platform, whilst also using it as regular computer.
ADobe requirements state 2GB for each LR & PS but recommend 8, is this 8 GB just in case of a "break glass for situation"
I am also looking at taking up studies in the graphic design field so that may mean using other adobe software in some regard.

Regarding Mac Book:
I have more less focused on getting a refurbished from apple store.
I can buy from apple store US and ship to Europe so the currency rate favors me.
Looking @ Retina display 8GB ram and icore 7 with 512GB flash storage on either unit,

The two choices either 13.3 or 15.4 have the same spec not including the screen size and price. As of now I have a 3GB 14" display windows laptop I went to my local apple store today and I had second thoughts on the 13.3.

Also what is a NVIDIA GeForce GT 650M with 1GB of GDDR5 memory and do i need it

Any advice appreciated thanks

( 55 people have seen this post and there has been no replies I never understand that forum phenomenon)