How much power do i really need?

Hi all!

Earlier this week the battery of my 13" laptop (i've had it since 2010) started to behave badly, really short battery times etc. So i have decided to buy a new one this week, i have tried to make a decision but got stuck on a couple of questions.

The reason i want a laptop is because i like to be mobile, and want to be able to work on the move even if i travel. The two laptops i choose between has the following specs:

13" retina 2,7 GHz dual core Intel Core i5 8 GB ram 256 GB PCIe-based flashstorage Intel Iris Graphics 6100

and

15" retina 2,2 GHz quad core Intel Core i7 16 GB ram 256 GB PCIe-based flashstorage Intel Iris Pro Graphics

The reason as to why this is a decision to make is because if i buy the 13" one i could buy a 27" screen for the times i work at home and still end up below my budget. What worries me is whether the 13" one has enough power for professional programming? (I am not yet a professional, i am still learning, so i have no clue of how much power my laptop really needs?) This also means that if i go with the 15" one it will also be the screen i use when i work at home.

Do i need the power of the 15" one, and for the times i am traveling, is the 13" one too small for a serious programmer?

I have tried google but haven't yet found the information i am looking for, so i decided to ask the Treehouse community as i know people here are really helpful. It's a lot of money so i hope you understand why i want it to get right in the first place.

So to finish up, do the 13" laptop have enough power to use for professional development work? And is 13" retina big enough for a serious developer working on the move(which i will do alot)?

Thanks in advance.