of course 8700K can clock to 5GHz without deliding.
browse on it ? yes
game on it under 80C? may be
run serious load on it without hitting thermal throttling ? may be.
Are you comfortable with CPU over 80C ? I'm not for anything but testing.
So yes, for 24/7 usage at 5GHz, deliding is probably required if lifespan is important.
Have any of the respected reviewers or moderators used this board with 5GHz overclock for something like encoding video continuously for few hours every day without active VRM cooling, let's say with AiO? Have the board survived a year ?
Yes, the VRM can not melt down, on this board the VRM has thermal protection. the system will simply turn off.
In previous post I already pointed my personal experience with overheating VRM. It is not limited to a single MB.
Do higher temps affect lifespan ? well, the solid capacitors will roughly triple their life span for every 10C drop. They are usually rated for 5-10K at 95-105C - really have no idea what type is used on this board.
So someone, using such board with serious 24/7 load is probable to experience failure within a year or two.
But yes, that math and considering that some people have above 30C room temperature and people that had MB failure/instability due to inadequate (no warning with fail scenario = inadequate/deception/crap) components is conjuncture. And there are motherboards with more than capable VRM with high enough efficiency that will not fail under continuous load. Manufacturers usually don't care about lifespan beyond warranty, they mostly care about profits. So making a board that will work for most people as cheap as possible, and replace failed ones within warranty is probably cheaper than making 100% stable one.
This gone way beyond topic. If you wish to call this MB good product, it is your opinion/vocabulary/religion. I have no problem with it.