rMBP 13'' late 2013 IRIS vs. 4k

Hello, Macforum

I currently own an IPS display with 27" and resolution of 1080p (LG IPS277L). Recently I've been thinking about upgrading to a monitor with a higher resolution since the PPI of my current monitor is pretty low. I've browsed through lots of stores and realised that prices of 4k monitors aren't much higher than prices of monitors equipped with lower resolution (1440p, 1600p etc.). I use my monitor mainly for work on my MacBook but also for games on my gaming desktop PC (with Windows installed) and occasionaly for gaming on Xbox One.
So far Dell P2715Q is the monitor I think would be the best for me. For about $550 you get a 27" IPS display with 4k resolution and 3 video inputs (HDMI, mDP and DP).
I heard that you will only be able to get about 52Hz at 4k resolution with rMBP 13''. I thought about maybe lowering the resolution a little bit so I could reach 60Hz. Do you think it would be possible? And what resolution would you recommend me?
And how about the other two devices? Which input port should I use for which device? I thought about using the HDMI for the Xbox, DP for the desktop PC and plugging the rMBP via mDP. Would it be possible or would there be some quality loss? What do you think apout the delay and input lag with the monitor I mentioned above. Will it be critical for gaming (I play lots of different kinds of games from sport and racing games to FPS)?

Thank you for your answers.


Specs:
Retina Macbook Pro 13" Late 2013:
8GB of RAM, 256GB SSD, i5 CPU (2,4GHz), integrated Iris 5100 graphics

Desktop Computer:
16GB of RAM, 256GB SSD, i7-3770, Nvidia GTX 760

Xbox One

 

Thank you for your reply.

As I said. The prices of 4k monitors seem to be only slightly higher than prices of 1440p monitors (at least where I live). Plus it will be better in the future when I will have a better PC that will actually be able to run 4k resolution at 60Hz. I am not planning on buying a newer MB anytime soon though.