I cannot believe it is so hard to find a good window snap for a 4k monitor!
I tried a few different snapping software and found gridmove is the most simple and customisable solution.
Windows 10 beta offers a better window snapping than 7 & 8 but its still not perfect.

I use a 4k 50" monitor primarily for programming and defiantly need the real-estate so i made my own simple custom grid and could not live without it! this layout aught to be integrated into every snapping software and even windows 10.

*'s represent triggers

corner triggers snap windows to a corners like the windows 8 corner snapping
*           |           *
|           |            |
|---------|----------|
|           |            |
*           |           *

left and right Edge Triggers snap the windows just like aero snap
|           |            |
*           |           *
*           |           *
*           |           *
|           |            |

The top has 4 triggers to snap windows verticaly (nice for programing!)
  *** *** *** ***
|     |     |     |     |
|     |     |     |     |
|     |     |     |     |  
|     |     |     |     |
|     |     |     |     |

all other spaces trigger into a 2x4 grid
|***|***|*** |***|
|***|***|*** |***|
| ---| --- | ---| --- |  
|***|***|*** |***|
|***|***|*** |***|
before using a 4k monitor I found my self using edge snap for everything... internet browsing, file exploring, and programming
So i and many others are used to living in half a 1080 monitor. the 2x4 grid allows me to use my 4k monitor like 4 monitors each having two halfs.

attached is a quick sample of what can be done in about 3 seconds

this firsts monitor is fully functional monitor 2 and 3 only have 2x2 grids