I hope I'm not bumping a thread that's done, but...it's recent enough and others have similar issues.
There are 4790K (and others going back to Sandy/Ivy) that simply get too hot. The primary culprit is the IHS (the can on top of the die). It is glued on with only thermal compound underneath. The older generation, and many of the higher end chips, are soldered to the die.
The glue may tend to expand as it cures, and perhaps Intel releases the clamps too early. Whatever the cause, it has been verified that the IHS occasionally shifts upward, away from the die, decoupling thermal contact. Those chips overheat no matter what we do.
However, many are just marginal. Good cooling will get fair performance. It's also been observed by a very few that over time the IHS may settled back down, under pressure from the HSF and due to heat. That is, some chips improve their thermal contact after a few weeks.
Many resort to removing the IHS. I'm preparing to do that to mine when materials arrive.
Yet, that's not all there is to it. 1.2 volts is too much for most 4790K's at 4.4 Ghz or lower. It appears that all boards assume a generalized profile, which can be updated with UEFI upgrades (sometimes to poor effect), and choose to feed more power than is required.
My stock, default settings, which ran turbo to 4.4Ghz and idle down to about 1Ghz produced 98C using OCCT on the stock Intel cooler, within about 90 seconds. A Coolermaster Hyper 612 v2 dropped that to about 87. I got that down to about 75c by setting everything to fixed mode operation. I'm at a fixed 4.4Ghz, 1.184v core, 1.7 on the main VRM, 4.2 Ghz on cache, 1.180v on cache, LLC around 50% (though it seemed to make little difference disabled).
I'm still learning this chip..well, Haswell and DC in general. It's touchy to get the right settings. I think it's more complicated trying to get adaptive modes tuned well, but I believe that's because the labels in UEFI on all the boards are difficult to understand.
Although my idle temps and power are higher than would be the case with adaptive voltages and speeds, my full load temps and power are lower than anything I could find with adaptive settings, and I couldn't stabilize the machine with adaptive settings even targeting the stock plan of 4.0Ghz with 4.4Ghz turbo. It would survive the tests, but in real world use I would have lockups/BSOD's. Once I switched to fixed mode and mapped out the chip's profile (voltage vs speed / thermal behavior) - the system has run for days without incident or reboot (72 hours since reboot, with multiple VM's, video transcoding, audio compression, RAR compression, 3DS Max editing / rendering, video editing, compiling in Visual Studio 2012...a bunch of stuff).