One of the important features I was looking for in my new laptop was the ability to drive a 4K monitor at full resolution and 60Hz. Basically when running Mac OS X, this means you get a 1080p looking resolution with pixel-doubled retina goodness! Nice for my aging eyes ;)
Apple’s website claims that the new 2015 13″ MacBook Pro can handle it, so that’s the model that I went for. But I had problems getting it running at anything higher than 30Hz on my Dell P2715Q 4K monitor. Turns out the problem was the cable that they include with the P2715Q. I purchased this well-reviewed cable on Amazon, hooked it up, and kaboom! I was running 4K at 60Hz. On the P2715Q, make sure to turn the MST setting off so that it uses the default SST setting.
May the 4K be with you, always. (until 8K)