If it was me, I would get the 750w G2 anyway. 100 watts more gives me a little piece of mind.

XrayMan
If it was me, I would get the 750w G2 anyway. 100 watts more gives me a little piece of mind.

Totally agree..And having a PSU that might be a little "overkill" will prolly run even more quietly because it's not working so much to output at or near it's it's rated specs and might even use less power from the wall too, not to mention leaving headroom should system components be added/upgraded (link).  

sahafiec
well, maybe I'm missing something. but what's the advantage to have a 750W PSU on a system that never uses more that 300-330W?
assuming the PSU's are most efficient at 50% load, it means I could get the best efficiency only during a coulpe of hours playing.
 
a quality 550W PSU already has an overhead, regarding my system, so why put a second 200W overhead?
am I missing something again? 

You'll be set for a while with the 750. You really don't have to upgrade the psu in the future if you upgrade the rest of your parts, like the video card/cards.

sahafiec
and a 750W Gold PSU will have no disadvantage compared to a 550W Gold PSU in terms of efficiency?

The only difference will be that you will have more watts, amps, aka more headroom in case you add more things down the road. There is no disadvantage of owning a higher psu then you need. 

that's exactly what I meant mdk7777777, I was starting to think I couldn't state my point right.
increasing the capacity of PSU shifts the max. efficiency area of the curve to the right for the same system.
that means the system falls to a less efficient area, it's not an extreme difference but it sums up at the and of the day.
 
for myself I'm sure not to build SLI, I just always stick to single GPU system. that's why I think more than 550W-650W is an unnecessary overhead.
regarding the brands we don't have Rosewill, Kinwin and Super Flower here at all. I know them from JonnyGuru's reviews though.
but recently we finally got EVGA  yet for the beginning only 850W, 1000W and 1300W available on the efficient side.
besides 600W Bronze is also available but I don't find 80+ Bronze up to date anymore.

Yeah I was talking about the gold units under discussion. G2.....but yeah if you are willing to pay for plat....or not yet released titanium. ...you can get better results down to 10%....
 
For example, this unreleased titanium superflower at 750 watts retains efficiency of 91% at 75 watt.
http://www.plugloadsolutions.com/psu_reports/SUPER%20FLOWER%20COMPUTER%20INC._SF-750F14MT_750W_ECOS%203991_Report.pdf
 
If evga were to market it, it would obviate the need for 450-550 watts, ...but would still not be inexpensive.
 
So, the cost/ benefit equation still favors a good 550 watt (PLat) at the same price as a 750 watt (gold)... if you are only going to run one card.
 
Example:
 
This superflower gold unit is on sale today for $47
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182261
 
which gets you 88-90% efficiency in the range of a single card.(say 75-350 watts)
http://www.plugloadsolutions.com/psu_reports/ROSEWILL%20INC._FOTRESS-450_ECOS%203115.1_450W_Report.pdf
 
In comparison, the evga 750 g2 only gets you 80% to 90% in that same range.
 
http://www.plugloadsoluti...OS%203724.1_Report.pdf
 
So you pay 2x the price and end up with lower efficiency.
 
The right sized PSU for your application will always be the most economical choice. ;)
 
The 750 watt Titanium will get you the efficiency, but most likely at 4x or more the initial capital cost.
 
You need to be folding or coining 24/7/365 for a shed load of years to get that money back from electric cost deltas.

mdk7777777Yeah I was talking about the gold units under discussion. G2.....but yeah if you are willing to pay for plat....or not yet released titanium. ...you can get better results down to 10%....

Ah, sorry - didn't realise you were constraining your statement to just the Gold units.
 

mdk7777777For example, this unreleased titanium superflower at 750 watts retains efficiency of 91% at 75 watt.

That is seriously impressive.
 

mdk7777777You need to be folding or coining 24/7/365 for a shed load of years to get that money back from electric cost deltas.

Indeed. By my calculations, to make it worth getting a Corsair AX760 over the equivalent EVGA SuperNova G2 (£35 difference), you'd have to use 200kWh more electricity (at 15p/kWh).  The biggest gap between the two in terms of efficiency is around the 50W load mark (84% vs 78%), which would be about 50 years of continuous use.  Alternatively, under load, the difference is only around 1%-2%, so under 600W of load, so that'd be ~25 years of continuous use (or 10 years at 700W).