Minimum recommended wattage with capacitor aging (off enermax site) is 560.
Beware: any power supply calculator is absolutely unreliable, and the so called "capacitor aging" concept, as it is presented by those calculators and similar sources, is also plainly wrong.
to 280w with gtx 680
which I replaced now with gtx 980
Frankly, if noise level/quality is paramount, I would go for an Enermax Platimax 500/600 (please note: I wouldn't do the same recommendation for their 750/850 siblings), if those PSUs had decent/fair prices there.
PSU in here essentially for 750w bracket same price for enermax and corsair (corsair like 8 usd more).
In 800d PSU has whole separate shelf so it doesnt get any hot air from other components (and rests at bottom).
But indeed I met with opinion that people do not trust passive PSUs on high end/oc PCs.
My advice was mainly acoustically-oriented: with reference to the overall sound signature, I'd rather an excellent fanned unit over any fanless one, that's based upon my own experience and personal preference.
Even reliability-wise that could be a smart choice, due to the minor stress imposed to electronic components: but that second advantage just could be (I mean, it's far from certain, talking about high quality units).
Eventually the choice of a PSU may be related to different requirements than just noise: talking about some SPCR-preferred options, performance wise a Seasonic XP/KM or a SF Leadex (like the EVGA G2/P2) are more probably that not better platforms than the ones used in a CWT/Corsair HXi or by any SF Golden King-based PSU, which in turn are better platforms than an Enermax Platimax, which in turn is better than the FSP platform used in the BeQuiet E10-series, and so on (please note that all the mentioned units/platforms are of at least decent build quality and very good performances and that price-wise such a list would look different).