bottleneck Don't know what to upgrade next? "Bottleneck issue"

[KnightTechQuery]

Hi! I've been deliberating for the past couple of weeks on what I need to upgrade next for the most performance for my money. Linus' latest video gave me the prompt to ask for advice here. Hopefully this is the right thread to ask this in.
I do very much want to avoid being bottlenecked, but as explained in the last video, I don't really think that will be an issue, rather that I'm not sure what will give me the most performance at this time, and not bottleneck my existing parts. 

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Specs:

Intel Core i5-7500 CPU @ 3.40GHz

MSI Z270 TOMAHAWK (MS-7A68) (U3E1)

G.Skill Vengence 16 GB 2133Mhz Ram

MSI (1462) GeForce GTX 960 2G

 

I made a sale purchase on the GTX 960, which is why it's such a weak one, and a dumb mistake on the locked i5 7500. I'm looking to start rectifying those mistakes. However, I can only afford a CPU & Mobo combo, or a new GPU at this time. At this time, the parts im looking at are: 

 

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Asus Prime Z370-P LGA1151 Intel Z370 Coffee Lake ATX & Intel Core i5-8600K 3.6GHz Hex Core 
The new architecture and 2 extra cores are great. And I'll finally be able to passively overclock my CPU for some increased performance. Or, 

 

Asus GeForce GTX New gen 20/1160 ROG-STRIX-GTX1060-O6G-GAMING 6GB if and when that comes out. 

 

 

I predominantly use my system to play games, in a variety of games. Probably more CPU intensive games like World of Warcraft, but a fair mix of other games as well. 

Note that whichever part I buy next, I'll buy the other one when I can afford it next. So it's not too much of an issue if the new part will bottleneck my existing parts only slightly. 

 

Any advice would be greatly appreciated! Have a great day. 

 

Edit: I play on a 1K 144Hz Samsung C24FG70 Monitor. Don't know if that will make a difference. 

[DudefromHamburg]

without any shadow of a doubt your GPU, Kaby Lake Quad Core i5 even though its a non K should run well enough. i guess you are going for 1080p, so CPU Bottleneck wont become much on an issue

 

ditch the mainboard and invest in the new gpu.

[KnightTechQuery]

4 minutes ago, DudefromHamburg said:

without any shadow of a doubt your GPU, Kaby Lake Quad Core i5 even though its a non K should run well enough. i guess you are going for 1080p, so CPU Bottleneck wont become much on an issue

 

ditch the mainboard and invest in the new gpu.

Thank you for the fast reply! I will most likely go with your suggestion. I just have one more question. You said that the kaby lake should perform fine, however I've been experiencing wierd input lagg in games like Pubg, and when I run WoW, my CPU will be maxed out more often on task manager than my GPU. Am I interpreting this wrong, or might there be an issue? 
I was also fairly convinced about the GPU upgrade, but those issues made me wonder if it's a CPU issue.