Upgrade CPU or GPU first?

[leoooooo636]

Currently I have an i3-6100 and a 1050ti.
I was wondering which should I upgrade first, my GPU to a 1070 or my CPU and mobo to an i5-7600k and an asus strix z270f and a cooler for the CPU of course.
Either of these options come out to around 400 GBP so I can only get one or the other.
Or is there maybe a lower i5 and a 1060 somewhere around that price so I can upgrade both.
I want to mostly play open world games like the witcher, gta v, the division etc on medium/high settings.
Any answers are appreciated.

Edit: My current mobo is an msi h110m pro-vd micro atx.

 

[Darkbreeze]

Upgrading the CPU without upgrading the GPU isn't going to offer you much in the way of gaming performance improvement because the card you have won't perform fast enough to make use of the new CPU. In other words, if you upgrade the CPU but not the graphics card, your performance is still going to be limited by the lower performance capability of the graphics card that is currently installed. Your current CPU is more than capable of handling everything that 1050TI can throw at it, but it will not work that way if you go the other way around.

Upgrading the GPU card first though will likely allow some improvement because the 2/4 Skylake cores on the i3 are fairly strong by comparison. Certainly you will have some limitations because you will still have a somewhat less robust CPU but later when you upgrade the CPU you will make that up again. So the only way to see increases in performance after EACH upgrade is to do the GPU card first.