i5-4690k vs. i7-4790k // GeForce 970 vs. 780

Literally nothing different between a i5 chip and an i7 chip for the most part other then hyper threading. yes more cores equal better rendering/photoshop/more applications open at once and i guess overclocking, but thats debateable. It's really down to the silicone lottery. That said, if you don't plan on upgrading for at least 3-4 years like me, then i'd wait why. Simple.

Broadwell chips have already dropped, so the 4690k/4790k devils canyon/haswell refresh are technically outdated already, that said so is broadwell this year actually this august skylake's going to be formally announced at the games developer conference so expect it to drop in a couple months so if you plan on building a pc, use the new updated microelectronic chip/die shrink. You should see about 10-20 percent gains over the previous generation i.e. haswell not so much on broad well maybe i'm not sure. Plus you have the added bonus of having the option to get ddr4 ram later on when it comes down in price because other than 6 core 5600k cpu's the only other consumer grade stuff that'll have ddr4 capable moba's/cpu's will be skylake. Don't worry you can also use ddr3 so i'd get ddr3 memory now and upgrade to ddr4 in a couple years when it's cheaper.

Gpu wise, i'd say go with at least a 980 i mean yeah the 780 is better then the 970 to an extent, but when dx12 comes along i believe 970's are 12.1 compatible so you should see some gains their. That said are you set on getting an nvidia card, if you're on a budget and looking for a price v performance type card i'd look at some of radeons line up. I've had a 7950 3gb windforce. For the better half of about 2 1/2 3 years and i gotta say it's a good card and an amazing value. Whats your price point on a gpu if your'e spending about 350-330 ish on a gpu go a radeon 390 saphire edition. 8 gigs of vram granted it's unnecessary unless you plan on crossfiring, but overall performance v price it'll beat whatever nvidia has. That said i did recently buy a 980 ti. So really a price point would help.

To resume the first answer:

I5 4690K and GTX 970

Even in older games, the gtx 970 is a faster card. It's newer as well.
http://www.anandtech.com/bench/product/1355?vs=1036

I'd opt for the 4690k + gtx 970. If budget allows, then consider the 4790k + 970. Most 4690k's are decent overclockers and can typically reach i7 speeds or even come close to oc'd i7 speeds with a decent cooler (something more than a $25 212 evo).

For purely gaming, the i5 is a good choice. With all the options available, a lot of people get stuck unable to choose, worried the i5 may not be enough. The 4690k and 4790k are both powerful chips. The i7 has hyperthreading which allows a slight performance increase that can vary in heavily threaded situations that can make use of it. It can allow up to 20% or so performance increase but that's a best case scenario. Just like some games actually perform a few fps better with it turned off on an i7, it's not guaranteed magic performance. I wouldn't consider devil's canyon 'outdated' because of broadwell just because at best broadwell is an efficiency oriented sidegrade. Skylake will be the next performance bump and will be interesting to see actual results. I don't put much faith in promises from either amd/intel thanks to their pre release hype in the past.

If you're actually playing a game, I'm going to be doubtful that you're actually working in the other browsers/windows. After all, people only have one mouse so it's kind of one or the other. Having lots of things open requires ram, not cpu. The memory is what holds open items (windows, browsers, tabs etc, along with the game) at the ready. The cpu only processes what's active and tends to put preference on the window that is either maximized or has 'focus' (aka the game when you're playing or the browser if you alt+tab to it or select it with the game on pause. If the game is paused while you're in the browser, the game isn't doing much but sitting there. It takes quite a bit to make an i5 struggle, the 4690k is a stronger cpu than anything currently in the amd lineup with the exception of maybe specific video rendering scenarios. Even then, it varies from one program to another just like games vary. If you're really that worried about multitasking causing slowdowns while gaming, shoot for 16gb of ram. An ssd will also help over an hdd if you run out of ram but is more or less a non issue if you have enough ram to begin with.

Games don't just come out overnight. They're a surprise to the consumer sure, but look at how long we know about them prior to their release, months before their release. The hardware manufacturers know even more than we do. If every other cpu except 8 core or 4 core/8 thread were so 'weak' they could barely handle web browsing, is it realistic skylake is coming out with brand new i5's in addition to i7's? They only update cpu's every so often, it wouldn't make sense to create chips that were rendered irrelevant so quickly. Nor would it make sense to design games that effectively killed half or more of the gaming machines and likely customers.

The big difference between a 970 and a 390x well i think 390x or 390 for that matter has newer architecture so essentially dx 12.1 or is .2 compatible which the 970 isn't . Generally speaking though from my experience the higher end cards tend to use more power with radeon then their nvidia counterpart at least with this generation. But not much other than that though amd is better for value then nvidia.

Regarding the difference between a 970 and an 390x. about 5.5 gigs of ram. 390x's have 8 gigs of gddr5 while 970's actually have 3.5 gigs of usable ram. I'd say stick with the 390x wait a few years and buy another one that way you're essentially future proofing. Games now a day's at least require you to share vram on multi gpu rigs and if you're gonna crossfire mine as well get the gpu with the most head room. So in terms of just raw performance 390x wins over a 970 anyday, in terms of v ram it also kills the 970 overall a 390x is a much better value over a 970.

Regarding the 970 over a 780. It comes down to architecture/power consumption. Basically as @synphul said, it's dumb for companies to make completely different tech every year the r&d costs etc. So they just essentially get new chips and tweak the programming for a lack of a better word and the 780's architecture is dated at least in comparison to a 970. Essentially yeah, a 780 is a good card now, but not exactly the best thing for the future, not knocking a 780 it's a great piece of tech but i'd get a 970.