4K 60Hz over DP with Late 2013 Macbook Pro 15" + Dell P2415Q? I have a Late 2013 15" Macbook Pro with discrete graphics. 

According to this Apple support page: https://support.apple.com/en-us/HT206587 this model supports 4K 60Hz over MST.

I just purchased a Dell P2415Q monitor, which supports DisplayPort 1.2, MST, and 4K 60Hz.

I have the two connected by the included mini DisplayPort to DisplayPort cable.

And the monitor is running at 30Hz.

Everything I've read suggests that I should be able to get the monitor to run at 60Hz, but I can't find out how to. I'm trying to find answers among all the search results, but they're either outdated, different models, or asking about HDMI.

Can anyone assist me?

EDIT: Here's the monitor's display options, which show that I've turned on MST and where I'm getting that it's running at 30Hz:
Okay so I got 60hz working at 4K. Despite the fact that I swear I already tried this, the key was turning off MST.

Unfortunately, I can't recall why I turned MST on in the first place. Did I create my own problem? I will say that I was unfamiliar with what Multi-Stream Transport was when I read the Apple support doc that I linked to in my question, and the doc was written in such a way to suggest that it was necessary for me to have on to get 60Hz on my MacBook Pro model.