Pros: Super fast in both multi-threaded and single-threaded tasks. Idles extremely cool. Strangely cool in fact, but in a good way.
Cons: Not quite the OC'er Intel wanted us to think it was. But has 4.0 stock & 4.4GHz boost, so that's ok. Runs warm when OC'ed.
The 4790k idles strangely cool, in the low 20's (C) with my Corsair H80i, and is about 8-10C cooler than an i7 4770k at idle all things being equal. And it stays around 45-48C under work load such as gaming, etc. It is a real beast of a processor.
However, overclocking is not as great as we thought it would be. I think Intel's early claims of a new improved TIM and voltage regulation was an exaggeration, and it still doesn't come close to Sandy Bridge's fluxless solder IHS. It may be better than the Haswell version 1.0, I'll give you that - but it's still not "that great." I forsee some serious delidding going on over the next few months on DC and much-much testing.
Once you get past 4.6GHz temps skyrocket pretty quickly into the high 80's and 90's(C) and thermal limits and throttling soon follow. Oh I'm sure there are a few golden chips floating around out there that will do 4.8GHz or even the magical 5, but they are gonna be very scarce. And you're gonna need a serious cooler like a H110 or similar to keep a small fire from igniting inside your case. The L2N enthusiast crowd may do better w/OC'ing though, well just have wait and see, wont we?
But IMHO to get a 4.0GHz stock 4790k CPU is really nothing to scoff at. That's a real nice jump up from a stock i7 4770k (3.5Ghz) and it makes for an incredibly fast stock chip. AMD doesn't have anything even close to this unless you want a 9590 Vishera which is a 220 watt TDP proc...seriously?). That's just sad because DC is an 88 watt TDP.
The i7 4790k will be top shelf for years to come, and I give it the highest recommendations. If you are starting a new build and want an i7, Devils Canyon and a Z97 board are the way to go. It's a no brainer.
Yes, I know it's a "k" part and should be more overclock friendly, but that's why I took off 1 star. And you can still push it some - and since each proc is a tad different, results will vary. Right now I'm just running my MSI Gaming mobo's "Enhanced Turbo" feature, which make its run at 4.4GHz all the time on all 4 cores. And it's stupid freaking fast! (the 250GB Samsung 840 EVO doesn't hurt either).
Just get this CPU NOW. Maybe you'll win the OC lottery.