mohitakundi :
The i5 4670 mildly bottlenecks my friend's 1070 OC.
1080 Ti ? Don't bother......
Get a 1080 and use the saved cash+a bit extended budget for a kaby lake setup
Don't forget that a few months ago, the 1080 was called by many "The Most Incredible Graphics Card Ever"
1080 is Decent Enough for 4K
Since you've ordered the 1080ti try to upgrade your system as soon as possible cause your i5 will soon struggle with the modern day 4K
I completely disagree.
1) The performance difference between the 3570K and the 4670 for gaming is 3-5 fps. Absolutely no noticeable gain in real-word performance. Haven't you heard that Intel has been coasting for the last five years while AMD was taking a nap? The new Kaby Lake will, again, be a few percent faster. Yawn. Upgrading a still very potent 3570K CPU will offer almost no appreciable improvement in gaming performance compared to splurging on the Ti. It's all about the GPU.
2) The 1080 is not that strong for 4K- it averaged about 55 fps across 15 tested games and dipped to 40 fps
( http://www.pcgamer.com/gtx-1080-review/ )
While certainly playable, that just cuts it today and things won't get any better down the road. That's exactly why a lot of folks waited for the 1080 Ti.
3) The 1080 Ti averages 68 fps across 16 games, dips to 50 fps. Much more playable and will not be outdated nearly as quickly as the 1080. It also has more vram.
( http://www.pcgamer.com/geforce-gtx-1080-ti-review/ )
4) You seem to misunderstand the nature of bottlenecking. The higher the resolution, the more the workload shifts
away from the CPU and is placed on the GPU. Therefore, the OP will have
less bottlenecking at 4K than (s)he would at 1440p or 1080p. I'd bet your friend is using a 1080p monitor.
Also, even a slightly bottlenecked 1080 Ti will still handily beat a 1080.
5) Yes, the OP should consider moving to an i7 for the next build, but right now it's a non-issue. 99% of the games out there are not coded to use hyperthreading.