I'm trying to decide between the $1999 13' TB with 16RAM vs the $2400 15' base model and I want to know when the discrete graphics card in the 15' gets turned on and utilized? The reason I want to know is because I want to get a second monitor (4K or 5K) and if the graphics card isn't needed or doesn't get turned on just for a screen or 2 screens connected, then I might not consider the 15' because the 13' has an Intel 550 internal graphics card, while the 15' has only a 530! If what I'm using the machine for doesn't require the Radeon graphics card then I want the machine with the better Intel internal graphics card. I don't do any video editing or processing. My current setup and use. I'm use my machine for browsing the web, watching some movies I download and I run VMWare Fusion with Windows 10 running Visual Studio 2017 RC to do all my development. I have a 22' Samsung 1080P monitor I connect to my current mid 2013 Macbook Air 1.7 Gz, 8Gb RAM, 500Gb SSD.