I'm not saying I could get anything as quiet as my Nexus Value, just that I don't see any point in spending £72 on a 525W PSU, which might not be powerful enough to run a Crossfire setup anyway.
A stock CF of 6950 won't draw any more than 290W DC (plus the system).
Oc'ed 6950s should draw more, up to 360W DC a pair: if you mind, you may do your math (surely it won't be quiet, nor cheap).
I think you've already read one of my usual data table from SPCR, but I would add some values for your convenience: PSUs tested at SPCR in last months up to ~500W DC.
Thanks for that.
I still haven't got round to buying a power meter yet, but perhaps we can assume that my system (excluding graphics card) needs about 200W, then with stock CF 6950 I'm looking at 490W and OC'd 560W. So a 650W PSU would be fine and avoid running it at full-tilt, which maybe isn't good for a PSU.
Now, when I'm not gaming, the system would be running below 200W, at which all four of the Value430, X-650, NX5000 (and hopefully NX6000) and Pro82+ are quiet enough, although the NX5000 and X-650 win.
Gaming with a single 6950 puts me in the 300-400W range, where the X-650 and Pro82+ win at 16dBA, the Value430 is close at 18dBA and the NX5000 is last at 22dBA.
With CF 6950s, in the 490-560W range, the NX5000(NX6000?) wins at 24-25dBA, the X-650 is 2nd at 31dBA, and the Pro82+ trails at 26-36dBA.
So clearly, for a single 6950 there's no point in replacing my Value430, whilst for a Crossfire setup (possibly) the NX6000 will be best, or if not it's a tossup between the Pro82+ or X-650 (which is louder at 400W but quieter at 500W).