Right now I have an early 2013 macbook pro with an external 24" monitor. Unfortunately this model won't do external 4k. For that I'll need to upgrade to at least the late 2013 model. I'm hoping to run at 60hz, with a monitor size 24" or bigger, and have the monitor cost $800 or less. I'll probably just get a late 2013 model unless I find a reason to go late 2014. If you have experience running an external 4k display on a macbook pro, what was the best combination you found while keeping cost in mind? Any help is appreciated!