If you're willing to take the chance, there's a tool that low cost, plus a tube of liquid metal, and ATV sealant, can jack the performance of the 4790K to 5GHz easily with less heat.
May need to feed a bit more voltage, yet many has delidded their Ivy Bridge & later CPU's with great success. Fortunately, we no longer need to revert to risky operations such as putting the die in a vise & striking a wood block with a hammer on the IHS to separate, or perhaps worse, the knife, which carries a safety hazard. All can be had for just over $50 shipped, which can be spread in cost if there's more than one owned that can benefit or (2) do it for someone else once you have the experience. My kit wasn't the first one I wanted, one from the EU that's constantly sold out, so settled on the Rockit 88 kit. I highly recommend that you watch some YouTube videos on how to do this before purchasing anything, so that you'll see what's involved, looks fairly simple, depending on which video you've viewing. As for me, don't care for the music, want to see the work.
I have three Haswells, to include both Devil's Canyon (4790K i7 & 4690K i5), as well as a i7-4770 that shipped in my XPS 8700. Have the tools, just haven't done it yet, have either been bedridden (am disabled), busy assisting others when I can, or working on my own computers, of which I have too many. These are mine, taken on my dining room table, my original work & not a copy/paste of another. I don't do business that way, on forums or in person.
BTW, for further proof it's my work, here's the 1st out of four sets of DDR3-2400 RAM purchased, wanted to try one kit before purchasing the other three.
Like you, I can get to 4.6Ghz fine by upping the multiplier, it's when I get to 4.7GHz & especially 4.8GHz, the BSOD's come in. Took me over 4 months & many BSOD's to break my own record on the HWBOT site with 1224 points, came within 2-3 points & one day, finally beat my previous by 3 points. I was once ranked in the top 1% of much everything, haven't participated as of late, yet will one this job gets done. You can go down the page & see my activity, also also the same set of RAM, submitted as a pic that proved I had purchased GSkill RAM.
BTW, I need to get one last item, although locally available, some clear nail polish. This should be applied in two thin coats (note that some uses Scotch tape instead & remove afterwards), I'd rather protect the die with a clear coat, am clumsy with tape & don't want any of that liquid metal to come in contact with the die. Also, while the RTV sealant is in a somewhat large tube, can use for other purposes, only a thin cost is needed to reseal the IHS. Some uses super glue, IMO, that can become a disaster should the job need to be redone in the future. There's circuits on the die, that super glue may break one & once that happens, all you have is an extra IHS, the rest of the CPU is useless. The RTV sealant is soft, only meant to seal, not a permanent bond, commonly used on valve cover, thermostat & other gaskets to prevent leaks, or to hold in place during assembly.
Maybe running at 5.0Ghz, your i7-4790K won't be a bottleneck. BTW, the 4790K beats it's successor, the 6700K in Passmark tests, this is amazing, especially considering it uses DDR4 RAM.
The i7-4790K was once Intel's flagship quad core CPU, if you can squeeze just a bit more performance out of it, won't bottleneck the 1080 FTW, doesn't my 1070 FTW during benchmarks (Heaven's Benchmark, Futuremark & others), you'll be fine while running lower temps by 20-30C as a result. I'm going to do some before & after benches, which will also show temps, will then be convinced that the effort is worth the time. Some has even repasted the IHS with MX-2 & laid the IHS onto the die in the socket and shown 20C dips, so am positive liquid metal will do the same or better.
Good Luck, no matter which way you turn, don't give up on the 4790K, it was Intel's last gift to those who made Haswell the longest running of the 'i' series to date (over 3 years). It can still hang, if the performance can be brought out of it. Will need some fine tuning to get to 5.0Ghz, and I'd like to think a bit higher, maybe 5.1/5.2GHz if lucky. Who knows, some chips are a bit better than others, yet I feel 4.6Ghz is way on the low end, should be 4.9GHz minimum (with delid & tuning). Some makes it to 4.8GHz with tuning only, but I don't trust that thermal paste to hold up, there's no substitute for metal to metal contact.