For me that is little higher voltage. I don't like to go over 1.300-1.350V but Ivy is very good on higher temps and little higher voltage.
Temps need to be close to 100C to start to make problems. Under 95C work without problems.
I'm not completely sure but I think that higher voltage even with lower temps could cause degradation and CPU will need more and more voltage for some clock. In that case only chance is to drop clock for 300MHz and hope to degradation stop. Example from 4.9 to 4.5GHz.
I was very happy with Z77 platform and today I think that Ivy is best from Sandy and Haswell mixed.
Not so good overclocker as Sandy, but not much worse and better on higher temps, but have more important improvements than 200MHz clock.
Native controllers, 200-300MHz better IMC are more important than average 200MHz lower OC capability than Sandy Bridge.
Thermal paste is minus.

I'm really sorry now because I missed that Maximus V Extreme.
That was very nice and stable motherboard and most owners are completely satisfied.
Sometimes I even check marketplace in my country if some used show up cheap to build backup computer.
I have everything other and i7-3770K 4.8GHz, only I want ROG Z77 Motherboard.
Even Maximus V Gene could serve good. But for now I didn't saw nothing near me on marketplace for normal price.
Not 50 euro cheaper than VIII series.

I run mine at 140 % , those are some good temps at 1.480v . I have my 3770k at 4.8 1.375v , im good with that .

Well if you have to go that high with the voltage for 5.0GHz it seems your cpu hit the wall or I a little weaker as you say, it would be better to run with 4.9Ghz. If you take the voltage up around 1.70v - 1.80v - 1.90v you will have a dead cpu instantly so don't take it any higher than 1.60v and even that is too high.

You can try Load Line Calibration in DIGI+ to HIGH this is 50%. Enable PLL overvoltage voltage or whatever it's called on the extreme tweaker tab, disable all power saving features. Enable extreme tweaking and super pi booster although I've read these just help with benchmark scores.

Not all cpu's are created equal so some will need more voltage and some will need less for the same speed. 16GB of 1600MHz ram shouldn't affect your overclock, enable X.M.P. and away you go.

If witcher 3 is crashing then try with 4.9GHz and raise the voltage until it no longer crashes. My cpu is game stable with the games I play but probably wouldn't pass a stress test.

Yeah disabling hyperthreading can help but I wouldn't recommend it., the witcher three probably uses 4 cores/8 threads.

You can take the voltage past 1.52v but it's risky and for an extra 100MHz it's not worth it but if you want to I'll tell you how. Just be aware you're doing this at your own risk and I in no way shape or form take responsibility for you damaging or frying your cpu. I fried my first 3770k with 1.80v+ and some might die before that.

To get past 1.52v, enable over voltage (I think that's what it's called) on the extreme tweaker tab, then on the monitoring tab set the cpu voltage to ignore.

It's risky and I will suggest sticking with 4.9GHz.