Decided that before I do more abuse of my 380X, I really need a new PSU.
I will probably buy a Corsair RM1000x tomorrow (people are now wondering, ***, why so many watts? well, it is because that is what for sale... I picked the first decent PSU on the list after ordering it by "cheapest first").
Did some more tests today anyway, after the 480 debacle, lots of people suggested undevolting the 480...
Well, I undervolted my 380X.
Impressive results, the throttling I complained previously, is even less now (but I didn't tested it that much).
More interestingly, -40mv and +20% power results in OCCT framerate jumping from 550 all the way to 605!
Also, in my research I found out the 380X has the same TDP and power limits (at least for reference, dunno about Sapphire Nitro) as the 380.
But the 285, and the 380, have less parts available for simultanous usage, and this DOES affect power usage (I remember once someone made a "mining bios" that worked by disabling ROPs for example? to make the cards more efficient regarding power usage).
The 380X has 15% "more chip" than the 380, thus theoretically would need 15% more power.
Also, both have stock clock of 970mhz.
Sapphire Nitro 380X has stock clock of 1040mhz, thus a 7% increase.
So, assuming (I know, bad assumption, but good for "back of the napkin calculation") the power usage is linear with both clock, and chip parts powered, the Sapphire Nitro 380X should need a TDP increased by 15% for the "X" chip, and 7% for the clock. This results in 23% (1.15*1.07)
This would explain why I needed +20% to make it stop throttling.
After I get the PSU, I will see if I can disable "Crimson Power Saving" (seemly Crimson has different handling of power throttling than Catalyst, for example Tom's Hardware review of the 380X, that I believe was still using Catalyst, saw it drawing 190W in Metro 4k Loop, but 255W in Furmark, while the expected behaviour in Crimson would be draw 190W in both situations).
And also I will see what happens if I use power limit of +50% after doing registry bios modding (ie: editing the powerplay table, but on the windows registry, instead of actually flashing a modded bios).
My objective is see if I can nail down that clock, make it NEVER throttle due to power, maybe even OCed.
Happily the 380X is seemly quite safe regarding that (during Tom's Hardware Furmark abuse, its PEAK PCI-e slot draw was 71W! and the average way below it!)
The 380X is seemly a great GPU, gimped by its bios and drivers, when "set free" maybe it can surpass a nVidia 970 in performance. (I would be VERY happy if that happened).