500W were no assumption, I measured it
Yeah, I knew. What I meant is 500 W might not be a very reliable "high watermark", but given that you are adding a 50% pad, you are taking that into account, albeit in a different way. When you asked about the subject, I did not know you were adding that amount
As my cards have cost 1000 Euros, I will not risk running furmark. It makes no sense anyway because this load is unrealistic and the 580 have over current protection enabled by default which is there for a reason.
Of course, furmark is not realistic, but I think it definitely serves as a high watermark for power consumption and can highlight VRM refrigeration problems. I feel that, once you measure what furmark needs, you have an absolute graphics card maximum you will never surpass in real life. Add 10/15% to be on the safe side, and you are set.
I think if I test with the highest load I can possibly give under realistic circumstances (Downsampling with 2560x2048 resolution, 8xSGSSAA and for instance Unigine or Crysis or something) and add to that a buffer of 50%, I'm good.
In fact what I found in my case is furmark adds that 50% over Unigine -amazing. I would use a larger pad, more like 60 or 65% just to be absolutely sure. By choosing the AX850 over the AX750 you are doing that
Concerning stability, there are better tests, because every software taxes the cards differently. It can happen that your setup is furmark stable but that it crashes in a game or gives you artifacts. Furmark is just good for testing temperatures.
Too true, IMHO furmark has an undeserverd reputation when it comes to stability testing. In my setup unigine finds problems much faster than furmark, and in many cases finds problems furmark never showcases. Nowadays, Furmark is only good to highlight power related problems, an interesting test when you use aftermarket coolers. I use an Accelero Xtreme Plus, so it is a concern for me.
Nevertheless I will get the AX850 as it costs just 18 Euros more than the AX750 and I don't know how much I will overclock the cards over their lifetime
That's a good PSU, but, as abula mentioned, I would not OC if you go for the AX850 (unless those 500W you measured are with max overclok, then everything is ok).
Just to make absolutely sure I'm not too far off, I checked current consumption under Unigine, not just furmark, which is enginereed to suck power and might bias the experiment. At stock speed, my core consumes around 36 amps and 52 at absolute max overclock (let's be safe), a whooping 44% increase. Granted, my VGA is a 5850, but... I would hate you spend so much money to find you are off by a mere 50/100 W.
Enjoy your little silent monsters