What are the biggest bottlenecks in the search for 4k 60fps gaming?

At this point in time almost any high end system (being reasonable here, not some entry level i5) will be limited graphically. This could change as time goes on, but at this moment in time a 7700k and 16GB of RAM wont be the deciding factor.

like any other scenario, this will be game dependent. but overall, the gpu is the main bottleneck. tom's did a review not too long ago and at 4k a dual core pentium gave the same fps as an i7 at 4k!! pretty well shows what the biggest issue is. obviously this is the not the best way to do it and a solid cpu is also needed, but the main problem is the gpu. just about any cpu can feed it fast enough to keep it very bust trying to pump out 4k frames.

think the only way i have seen it possible was with more than one high end gpu. at least 2 1080's. a single pascal titan x was not enough for every game to hit this goal either. well with max settings anyway, you can lower settings and hit this number with a single 1080, but most folks seem to be fixated on max settings as if it is not worth playing without it.

Hi,
1) It very rarely makes sense to game at 4K anyway. You can run most games at 2560x1440 and have it scaled to 4K on the monitor with similar visual fidelity to native 4K.

2) GPU. Yes, this is usually the limiting factor, and unfortunately that may mean buying TWO top-end cards (like 2x GTX1080 in SLI). However, not all games support this and when they do there may be stuttering introduced.

*So unfortunately, there are people with two high-end graphics cards that have a LESS enjoyable experience in some games because they got the second card. They got an arguably nearly IDENTICAL visual experience in terms of the quality of each frame but again stuttering (game not smooth).

DX12 and Vulkan games will eventually use multiple GPU's properly (to both work on the same frame, not one per frame), however that probably won't start being common for at least two years. That needs to be baked into the game engine but it's a difficult problem especially whilst maintaining backwards compatibility with DX11. So I recommend a SINGLE GRAPHICS CARD.

3) 4K HDTV and 4K monitor is not the same BTW.
AFAIK with an HDTV you can't choose a resolution like 2560x1440. So you're forced to run at 1080p or 4K. That almost always will be 1080p as game smoothness is more important. Plus, if you aren't sitting really close the game might not even benefit from 4K resolution.

4) TWEAKING the game settings goes a long way too. Often there are settings which are really taxing that don't add a great deal visually. You have to experiment.

You should learn how to use Adaptive VSYNC as well. It turns VSYNC ON and OFF automatically. On 60Hz monitor aim for minimal (i.e. 5% of time) drops below 60FPS. When it does drop you get some screen tearing but not added STUTTER due to the sync mismatch by having VSYNC ON but not being able to keep up.

5) GSYNC - for desktop monitors, GSYNC is a bit expensive but also provides a smooth experience. The monitor only draws a new frame when the GPU sends it one rather than updating at exact intervals (i.e. 60x per second). This new, asynchronous method prevents screen tearing, reduces lag and prevents stuttering (VSYNC type of stuttering at least).

Example monitor: GSYNC, 144Hz, 27", IPS ($800USD?)

For a shooter I might aim for about 100FPS average. Some games need a 60FPS cap.

A good example of a PC for that would be:

i7-7700K (or RYZEN 4C/8T CPU)
16GB (2x8GB) 2666MHz DDR4
GTX1080 (or similar AMD Vega GPU later)
etc.

It depends on the game.
With a GTX980ti, I generally run at 60 fps on civ 4/5, skyrim and flight simulator on a 4k monitor.
CPU is I5-6600K@4.8 which is almost as good as it gets.

Fast action games may not fare as well.

My motivation for 4k was a 40" monitor which is very immersive.

My suggestion is to buy your 4k monitor first and then see how you do in the games you play.

Hello, I just wanted to mention that

3) 4K HDTV and 4K monitor is not the same BTW.
AFAIK with an HDTV you can't choose a resolution like 2560x1440. So you're forced to run at 1080p or 4K. That almost always will be 1080p as game smoothness is more important. Plus, if you aren't sitting really close the game might not even benefit from 4K resolution.

actually depends on the hdtv you own as I own a Samsung 1080p tv. When I hook it up to my laptop I am actually able to choose multiple resolutions besides 1080p and 720p on my Samsung tv just like computer monitors.

a quality one should be enough. they are only 225w or so for average model. 250w for the top end ones.

but be sure your psu has the right connections. here is a list of the models available and their power needs to make it easy to research

http://www.tomshardware.com/forum/id-3047729/nvidia-geforce-gtx-1000-series-megathread-faq-resources.html#17902598

Yes, assuming the GTX1080 cards are not overclocked power hogs requiring 2 8 pin pcie power.
http://www.realhardtechx.com/index_archivos/Page362.htm

And... quality counts.
Buy only tier 1 or 2 from a list such as this:
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

I have no problem overprovisioning a PSU a bit. Say 20%.
It will run cooler, quieter, and more efficiently in the middle third of it's range.
A PSU will only use the wattage demanded of it, regardless of it's max capability.

even the 2 x 8-pin models only hit about 250w under gaming load. 275w or so on torture load but we know that's higher than real world will get to.

assuming it is quality psu, i'd have no concerns with 850w for 2 1080's. especially with the lower powered cpu's we got now.

Actually i don't think you need that much wattage... a 750w psu will do the job just fine for less money. Here's my recommendation:
https://pcpartpicker.com/product/dMM323/evga-supernova-g3-750w-80-gold-certified-fully-modular-atx-power-supply-220-g3-0750

here's a review from the reputable jonnyguru: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=500

corsair's RM series are really not that high on quality. don't get me wrong they're good but not that good at it's current price. did you take a look at the psu i suggested? well if you are not happy with 750w here is the 850w version. top quality psu for just like $10 more than the corsair one

Regarding your question: save money and get a k series i5 (ex: i5-7600k) by no way this cpu will bottleneck your gpu and it will give you same performance as an i7. games only care about cores, PHYSICAL cores not virtual ones so loosing hyperthreading doesn't matter when it comes to gaming.

gtx 1080 in sli will certainly give you the glory of 4k 60fps but mind the problems that may arise in multi gpu config.