You're right in the sense that the EVGA squeezes out cooler temperatures, but both units are manufactured by Asetek. Thank you for informing though, appreciate it. I should've done my homework.
I would go with the EVGA variant. I've heard nothing but good stories about their Customer Support, if you even need to contact them in the first place. My vote goes towards the EVGA option.
So is the EVGA..and the Gigabyte version... EVGA uses the same circular Asetek designed pump / block unit as the Corsair & MSI option. Gigabyte uses a CM designed unit, as can be noted by the square design and ribbed tubing.
Give it a shot, it can't hurt. 80C is pretty good for a max spike temp, and if you say your fans are only at 800 RPM, then you've got a bit more room to play with, not that normal usage will ever get you as high temps as a stress test anyways.
1.33v is pretty toasty as it is, I would try 1.35 at the most and see what clock speed that gets you. Although if you have to go beyond 1.35 to achieve 4.7 or 4.8, then I would leave it at the 4.6 (1.33v) you currently have.
I'm not sure what you disagree with. I'm saying that 200 MHz is not worth the possible voltage increase needed to achieve stability with it, however if no additional voltage is need to achieve an extra 100 - 200 MHz, then by all means OC that puppy.
Jumping from 4.6 GHz to 4.7 or 4.8 is not worth the possible instability and extra heat (If extra voltage is needed to achieve stability) for a trivial 200 MHz. 200 MHz will not make a huge difference, at least not as much of a difference going from 4.0 GHz to 4.6 GHz does.
I know this seems too simple, but I would first and make sure you have a proper mount on your CPU. 98C is way beyond AMD spec and I would imagine it would have shut down due to thermal issues long before reaching 98C. What motherboard do you happen to run the 860K with? Is your thermal paste applied correctly? Is your CPU fan spinning and at an adequate speed? If none of the above is the issue, then I'm afraid you may have a dud chip and you should contact AMD or the re-seller for a replacement / RMA.
I'm pretty sure it's a direct Mayhem's Pastel re-brand, I use Mayhem's Pastel Blue in my build here. I've had no issues in the ~6 months of using the stuff.
Those have completely different dimensions, not to mention the four mounting holes around the GPUs are most likely not the same. You would need an extensive amount of modding.