It would seem that after 500 installations, the data would seem to support your real-life experience.
How did you know to ignore the manufacturer’s design specs before these 500 installations and that accumulation of experience?
I did not, when I started I was way within speck. There was very few panels exceeding 37Voc, As panels advanced I used bigger and bigger testing and monitoring the results. I am still comfortable with 3s 49Voc , because I collected data as panels advanced.
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On this topic, I am somewhat fascinated by this rise in voltage, because as far as I know, the chemistry hasn’t changed much, and we’re still making 72-cell panels (right?). The Vmp therefore should still be around 36V (0.5V per cell), and the Voc should still be around 47V (0.65V per cell). Unless the advances in efficiency (do they dope the silicon with a different mixture now?) is also giving rise to this increase in voltage.
I think this is it. Is PERC not the big one that caused an increase in voltages?
Googling around a bit, …
From here:
A higher base doping leads to a higher Voc and lower resistance, but higher levels of doping result in damage to the crystal.
So doping definitely has something to do with it. And PERC cells are indeed more heavily doped. From here. That means they degrade a little faster in the first year, but has overall better efficiency.
I’m really terribly out of the loop on this stuff…
It does look as if the temperature coefficient didn’t change dramatically. That’s still around -0.3%/°C.
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Cloud edge effect will also raise Voltage, but again from operating voltage, most probably on a summer afternoon in Pretoria after your panel has reached 65-70 degrees C. By that time your array will sit at around 137 Volts, still a long way to 150.
I get that you are worried that your MPPT will pop, If it gives you peace of mind, I recommend you go for the 250/100 and string 4 panels per string.
I just checked, my panels have reached a maximum of 48.4V from an advertised Voc of 49.6V, and that was achieved 2 weeks ago, at 14h20. (I only have high res data starting from late last year).
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One example. 150 with 3s 460 watt JA solar over the last week (nice and cold) Never once reached 140Volt with a max of 139.68V for this week.
Two weeks back max of 135v
Three weeks back max 138v
Four weeks back max 136V
Five weeks ago max 140.03V
Six weeks ago max 139.78V
Example 2 in Pretoria. 12 x 550Ja Solar 3s 4p
Last week max 134.5V
Week before max 137.04
Week before max 137.54
Week before max 134.34
Week before max 135.32
Week before max 134.47
Guys I don’t want to be funny or pushy, but once I posted the real life data, the conversation ran dry… Why???
I think everyone has made the point they wanted to make.
Your real-life data shows that it is unlikely, perhaps extremely so, that a 3S configuration with current panels will exceed a Voc of 150V. It does not prove that it is impossible, in the same way that the fact that no-one has ever seen a pink elephant in the Kruger National Park does not prove that there aren’t any.
I personally see both sides but I wasn’t going to take a chance with my VOC of 49.9v.
Your figures are for VMP’s which is different measure.
I have also find the temperature of the 250/100 is lower (alot) running half pace than the 150 running full. So that gives more peace of mind that I’m not stressing the kit to much. I ran a 150/60 3s3p for a long while until budget allowed and won’t do that again (stress related 
)
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Yup. At this point the OP can decide how far he’d like to push the envelope.
(Of course, no matter how hard you push the envelope, it is still stationary. Ba-dum-tish).
Is this a reference to our failed postal service? 
The only 2 observations I will make: With the logging to VRM being once a minute I don’t think you will have very high resolution, here is a example from yesterday on a install that you actually helped us with in Pretoria 
As you can see the highest voltage appears to be 165.15V
But if I look on the controller itself the highest voltage for yesterday was actually 170.34V
Then my last comment would be: There is a reason why we build houses based on the 50 year flood line.
Even if it’s a once in a 50 year event you want to know you will be safe
Best post I read all day, thanks for all the views and comments!
This is extremely informative having regard to my question the other day about panel configuration on my flat roof.
Why I’m now just the teeniest bit upset now, is because now I’m wondering if I should splash out on a further 2 panels to do 3s on a 150 MPPT. ( en ek het nie meer geld nie!)
Julle blerrie boggers! 
Rabbit hole this solar thing. Never ends!